1 letter:
.

2 letters:
ad, pa

3 letters:
aim, air, ban, box, bus, cry, dip, ftc, ipo, job, lin, phs, pub

4 letters:
adam, bare, bawl, bill, card, expo, fail, fame, fare, fear, file, fisc, flnc, hack, high, left, luce, mall, mann, mart, mold, open, park, play, poll, post, riot, road, show, sign, spin, talk

5 letters:
amble, augur, banns, board, break, coach, crier, debut, disco, float, force, forum, glare, image, intro, issue, judge, light, local, men's, peace, place, plain, plaza, pound, rally, roada, route, rowdy, slate, telco, train

6 letters:
admass, advert, auspex, bagnio, burnup, busker, casino, censor, church, closed, common, cruise, direct, expose, filing, foment, gagman, gibbet, impart, infamy, jitney, junket, jurist, lector, let on, litter, lounge, lyceum, medium, minyan, notice, paging, piazza, polity, poster, potboy, potman, pr man, ramble, reader, report, reveal, riding, saloon, secret, sector, seized, stocks, streak, stroll, talker, ticket, unveil, vendue

7 letters:
affairs, agitate, antenna, artiste, auction, autobus, bahaism, bouncer, bubbler, bursary, canvass, carrere, charity, coroner, display, dissent, divulge, dry run, edition, enquiry, exhibit, express, festoon, gagster, gardner, general, hanging, impeach, inquiry, jobbery, justice, latrine, lecture, let out, lidless, liturgy, mailbox, niqaabi, nominee, obloquy, omnibus, opinion, painted, pillory, placard, popular, postbox, posting, preview, profile, program, protest, publish, put out, raucous, reading, recital, release, saunter, service, showing, showman, shuttle, speaker, stir up, subsidy, support, surface, utility, utterer, vespers, visible

8 letters:
assembly, audience, basilica, bulletin, cadaster, cadastre, carnegie, chancery, citation, contrary, cover-up, cuspidor, cutpurse, dedicate, disclose, discover, disorder, dominant, endorsed, evensong, exoteric, exposure, fan mail, favorite, gin mill, giveaway, incident, indurate, informed, lecturer, litterer, mandarin, maya lin, monument, motorbus, muckrake, national, newspeak, off-road, offstage, palestra, parkland, pollster, pothouse, premiere, pressure, promoter, pro bono, publican, publicly, quaestor, reckless, register, restroom, rhetoric, speaking, spittoon, squawker, streaker, taphouse, treasury, triumvir, turn out, versicle, washroom, write-in, write up

9 letters:
ad agency, backstage, bathhouse, bring out, calculate, candidate, canvasser, certified, charabanc, chokehold, condemned, conductor, debarment, detective, diplomacy, dog pound, favourite, gagwriter, give away, gladiator, haranguer, homestead, hot issue, hot stock, introduce, in public, left wing, limelight, litterbin, litterbug, manifesto, methodism, objection, orphanage, palaestra, pa system, poorhouse, programme, promenade, protester, publicise, publicize, published, pub crawl, ragpicker, regulator, rehearsal, sensation, spillover, spotlight, symposium, therefrom, unadvised, unethical, vulgarise, vulgarize, walkabout, wash room

10 letters:
advertised, appearance, attraction, birthright, blazon out, campaigner, commitment, confession, confidence, confiscate, corruption, disconnect, don't-know, exhibition, exposition, free house, generalise, generalize, highschool, impresario, land grant, letter box, magistrate, manipulate, market day, men's room, motorcoach, muckraking, opprobrium, park bench, pickpocket, plebiscite, poll taker, popularise, popularize, publically, public eye, public law, recitation, reputation, semipublic, slush fund, squawk box, statecraft, subsidised, subsidized, suppressed, taken over, tea garden, town crier, undesirous, unsolvable, verbaliser, verbalizer, visibility, voting age, vulgariser, vulgarizer, water-rate, waterworks

11 letters:
advertising, advertizing, agoraphobia, agoraphobic, bus company, bus service, celebration, chucker-out, closed-door, confiscated, convenience, declaration, dirty linen, discotheque, enlightened, gas company, gas service, gender role, headcounter, high school, horace mann, impeachment, land office, letter bond, litter lout, malfeasance, marketplace, market town, mass medium, officiation, open letter, p.a. system, pamphleteer, populariser, popularizer, powder room, press agent, promulgated, publicizing, public debt, repudiation, requisition, robert adam, senior high, spinmeister, spin doctor, stock issue, straphanger, triumvirate, trustworthy, tub-thumper, ventilation, ward-heeler

12 letters:
announcement, annunciation, appropriated, arrival time, auction sale, backgrounder, bully pulpit, closing time, commendation, condemnation, demonstrator, denouncement, denunciation, desensitized, elocutionist, eton college, expropriated, gambling den, gaming house, ground swell, gutter press, highway code, introduction, ladies' room, letter stock, malversation, market cross, money supply, nazification, opinion poll, presentation, proclamation, promulgation, public house, public works, revenue bond, rights issue, school board, service club, shamefulness, speechmaking, thoroughfare, transit line, unsuspecting, utility bond, victoria day, waiting area, waiting room

13 letters:
accommodation, advertisement, advertizement, amicus curiae, anachronistic, assassination, beatification, cause celebre, civil servant, communisation, communization, demonstration, dirty laundry, display board, display panel, double-decker, embarrassment, establishment, expropriation, fare increase, gambling hell, head of state, light company, litter-basket, litter basket, manifestation, market square, meeting place, national park, perambulation, phone company, phone service, power company, power service, publicity man, public domain, public nudity, public toilet, rapid transit, secret ballot, social phobia, solemnisation, solemnization, statesmanship, tavern keeper, trial balloon, vulgarisation, vulgarization, wanted notice, wanted poster, water company, welfare state, whipping post, whistleblower, works program

14 letters:
charter school, chief of state, civil engineer, closed session, departure time, divine service, eminent domain, gambling house, lost-and-found, medicaid funds, mixed nuisance, nonproprietary, penal facility, political hack, popularisation, popularization, pronunciamento, public charity, public lecture, public library, public opinion, public service, public transit, public utility, railroad train, scandalousness, self-appointed, sensationalist, silent partner, street clothes, transportation, virginia beach, water fountain, world premiere

15 letters:
andrew carnegie, ballyhoo artist, church building, comfort station, commercial bank, common nuisance, disgracefulness, exhibitionistic, fifth amendment, gambling casino, highway robbery, ignominiousness, insider trading, letter security, open-air market, orphans' asylum, performing arts, petty apartheid, public-spirited, public defender, public easement, public lavatory, public nuisance, public security, public speaking, public violence, rights offering, school district, surgeon general, time of arrival, toilet facility

16 letters:
clare booth luce, electric company, initial offering, intercom speaker, medical examiner, panel discussion, sleeping partner, transfer payment

17 letters:
civil engineering, close corporation, community service, drinking fountain, executive session, full service bank, indecent exposure, national monument, official immunity, oral presentation, park commissioner, penal institution, public discussion, regulatory agency, religious service, telephone company, telephone service, time of departure

18 letters:
advertising agency, anti-masonic party, appropriation bill, asbestos abatement, board of education, board of selectmen, closed corporation, in the public eyep, machine politician, mass rapid transit, private foundation, public convenience, senior high school, special assessment, subscription right, winchester college, write-in candidate

19 letters:
disreputable person, friend of the court, insider information, invasion of privacy, john merven carrere, private corporation, public opinion poll, recreation facility

20 letters:
conflict of interest, housing commissioner, open-air marketplace, public relations man, regulatory authority, teaching certificate, utility revenue bond

21 letters:
financial institution, public address system, recreational facility, teacher's certificate

22 letters:
field press censorship, financial organisation, financial organization

23 letters:
initial public offering, public relations person, redevelopment authority

24 letters:
clear and present danger, federal trade commission, isabella stewart gardner, master in public affairs, mortgage-backed security

25 letters:
public-relations campaign

26 letters:
privately held corporation, public-service corporation

35 letters:
united states public health service

36 letters:
national liberation front of corsica