3 letters:
ruf, aue, bao, bow, cao, cau, cow, dao, dow, fao, gow, hao, hau, how, kao, kau, lao, lau, mao, now, pao, pow, rao, rau, sao, sow, tao, vow, wow, yao, yow

4 letters:
buff, cuff, duff, guff, huff, luff, muff, puff, ruff, tuff, arau, avow, blau, brau, brow, chao, chow, ciao, dowe, frau, gnau, grau, howe, liao, luau, meow, ndau, pfau, plow, powe, prow, qiao, scow, shao, skow, thao, thau, thou, tsao, xiao, zhao

5 letters:
acuff, ahruf, anruf, bluff, boeuf, bruff, buffe, chuff, cluff, cuffe, druif, fluff, gliff, gruff, hofuf, hough, hufuf, knuff, muffe, pluff, rough, ruffe, saiph, scuff, shuff, sluff, snuff, spdif, stuff, tough, uw hf, vakuf, vdiff, yusuf, aarau, allow, bacau, blauw, bough, cacau, cahow, chiao, cibao, cocao, dadao, devow, endow, fuyao, graue, hmpao, hsiao, jwoww, kapow, klaue, kough, lanao, lmfao, locao, lough, lubao, macao, macau, mcdow, ogowe, pegao, podao, pough, pudao, qipao, sadao, schow, shrow, simao, sough, sprow, strau, unbow, unnao, vdpau, wodao

6 letters:
aufruf, ausruf, babeuf, dms af, elbeuf, enough, gc maf, mcduff, rebuff, rla pf, s/pdif, schuff, scruff, shruff, slough, spliff, stough, titeuf, vbe af, vse af, ahegao, al-fao, anyhow, apayao, atyrau, bajaao, bandow, bilbao, blough, bowwow, brough, cabiao, carwow, cedeao, clough, crough, curaao, daopao, depauw, dessau, drough, fernao, filyaw, i-thou, ifugao, initao, kowtow, kuntao, landau, latiao, lmmfao, maicao, maomao, margao, miagao, nandao, outbow, pathao, plough, powwow, prough, rizhao, schlau, serowe, sestao, shimao, shitao, shough, siopao, sorkow, taobao, tumbao, xinyao, youdao, zschau

7 letters:
auspuff, besnuff, cdf lif, dayhuff, earmuff, gccs af, gcss af, leboeuf, lebouef, macduff, magaluf, schliff, unstuff, xtratuf, and how, ant cow, bow-wow, brandow, cabuyao, cacajao, cainiao, carabao, curacao, dazibao, disavow, ehefrau, eyebrow, foclmao, guandao, hofbrau, huludao, humacao, jarchow, jiandao, lessnau, mandaue, miaodao, nanzhao, nylghau, pingyao, pow-wow, purewow, qingdao, roflmao, safflow, sea cow, shaohao, somehow, strough, tamarao, til now, todd-ao, toutiao, tpe wau, warehou, wikihow, wow-wow, youtiao

8 letters:
bumfluff, dyestuff, farabeuf, godbluff, handcuff, mcgeough, outbluff, overruff, petstuff, tartuffe, amy chow, aschgrau, barbakow, cash cow, cat chow, changdao, chingtao, disallow, disavow', feldgrau, hausfrau, highbrow, jungfrau, just now, kitaotao, know-how, krakatao, ling-pao, liuyedao, mahilyow, maranhao, marianao, milk cow, mindanao, monschau, neelghau, overcrow, rotflmao, rotglmao, rowdydow, schlough, shen-pao, shou-lao, sillyhow, snowplow, tian tao, tien-pao, tongliao, tsingtao, yarbough, zhenniao

9 letters:
abudefduf, creampuff, feedstuff, fisticuff, foodstuff, get-tough, get tough, goodnough, hot stuff, neck ruff, overstuff, piedboeuf, powerpuff, puff-puff, sob-stuff, sob stuff, chow chow, conceicao, dairy cow, eigengrau, first cow, hongyipao, kabeljauw, lichtblau, mike howe, milch cow, mouth bow, right now, sound bow, speak now, turnbough, until now, up to now, yanmaodao, yaorenmao, yiguandao, zhanmadao

10 letters:
breadstuff, cream puff, greenstuff, hufflepuff, jigglypuff, powderpuff, real stuff, roughscuff, semi-bluff, semi-tough, bella ciao, cheng xiao, goodenough, guilinggao, liang chow, middlebrow, morgenthau, pathet-lao, puppy chow, sacred cow, snowplough, take a bow, violin bow

11 letters:
counterbuff, good enough, in the buff, powder-puff, scottsbluff, small stuff, soon enough, sure-enough, sure enough, well enough, andrew howe, caniapiscau, geforce now, gong lijiao, he bingjiao, huang zitao, lister plow, maguindanao, qinhuangdao, recurve bow, shi tingmao, xiantiandao, xiaolongbao

12 letters:
oddly enough, off-the-cuff, off the cuff, sip-and-puff, trouser cuff, breastplough, here and now, maschinenbau

13 letters:
oeil-de-boeuf, anhalt-dessau, coco de macao, lister plough, martin landau, springing cow

14 letters:
oeils-de-boeuf, opchanacanough, opechancanough, changpeng zhao, manny pacquiao

15 letters:
anne-marie duff, athletic bilbao, john allen chau, schering-plough

16 letters:
curiously enough, strangely enough, charlotte nicdao, holier-than-thou

17 letters:
marshmallow fluff

20 letters:
interestingly enough

21 letters:
create from raw stuff

23 letters:
the world is not enough