6 letters:
batres, caters, gaters, gators, haters, laters, maters, matres, paters, raters, taters

7 letters:
craters, fratres, gaiters, graters, platers, praters, skaters, slaters, staters, stators, waiters

8 letters:
creators, curators, debaters, dilators, donators, equators, gyrators, levators, locators, mutators, relators, rotators, slater's, stater's, traitors, waiter's

9 letters:
actuators, adulators, agitators, animators, curator's, debator's, deflators, deviators, dictators, educators, elevators, emulators, epilators, expiators, fellators, hydrators, imitators, inflaters, inflators, isolators, iterators, mediators, migrators, narrators, operators, pronators, pulsators, radiators, testators, valuators

10 letters:
abdicators, abnegators, abrogators, activators, alligators, allocators, amputators, annotators, aspirators, cogitators, decorators, dedicators, defecators, delegators, detonators, dominators, escalators, estimators, evaluators, excavators, freighters, fumigators, generators, gladiators, hesitaters, incubators, indicators, inhalators, innovators, insulators, irrigators, litigators, meditators, mitigators, moderators, motivators, mutilators, navigators, nominators, numerators, obligators, operator's, operators', peculators, regulators, renovators, resonators, rotavators, ruminators, separators, simulators, supinators, tabulators, tailgaters, tolerators, venerators

11 letters:
abominators, alternators, applicators, arbitrators, attenuators, buccinators, calculators, calibrators, carburetors, celebrators, circulators, coagulators, collimators, commutators, cooperators, cultivators, defalcators, delineators, demarcators, deprecators, depredators, desecrators, designators, devastators, dumbwaiters, duplicators, ejaculators, elaborators, eliminators, enumerators, eradicators, evaporators, extirpators, fabricators, fascinators, formulators, fornicators, generator's, headwaiters, hibernators, inculcators, inoculators, instigators, integrators, legislators, liquidators, lubricators, negotiators, officiators, originators, oscillators, oxygenators, penetrators, percolators, perforators, pollinators, postulators, procreators, propagators, regulator's, regulators', repudiators, respirators, retaliators, speculators, stimulators, stipulators, subjugators, syndicators, terminators, translators, ventilators, vindicators

12 letters:
abbreviators, accelerators, accumulators, adjudicators, adulterators, annihilators, anticipators, appreciators, arbitrator's, arbitrators', articulators, assimilators, capitulators, co-operators, cogenerators, commentators, compensators, conciliators, confiscators, coordinators, deactivators, decelerators, deliberators, demodulators, denominators, denunciators, emancipators, emasculators, equivocators, exaggerators, facilitators, flagellators, illuminators, illustrators, incinerators, infiltrators, inseminators, intimidators, invigilators, lachrymators, legislators', manipulators, masturbators, negotiator's, negotiators', nomenclators, obliterators, perpetrators, perpetuators, promulgators, rejuvenators, summercaters, totalizators, trafficators, vasodilators

13 letters:
amphitheaters, amphitheatres, appropriators, co-ordinators, collaborators, commemorators, commentator's, concentrators, conciliator's, consolidators, contaminators, demonstrators, dissimulators, exterminators, facilitator's, impersonators, incarcerators, incorporators, interrogators, investigators, orchestrators, perambulators, perpetrator's, pontificaters, precipitators, proliferators, reciprocators, refrigerators, remonstrators, resuscitators, scintillators, second-raters, sequestrators

14 letters:
authenticators, defibrillators, discriminators, disintegrators, electroplaters, forty-eighters, interpellators, investigator's, investigators', monochromators

15 letters:
administrator's, administrators', bronchodilators, differentiators, excommunicators, neuromodulators, procrastinators, prognosticators, superfreighters

21 letters:
chernobyl liquidators

27 letters:
list of roman amphitheatres