2 letters:
og

3 letters:
bog, cog, dog, fog, jog, log, ogg, pog, rog

4 letters:
acog, agog, blog, clog, flog, fogg, frog, grog, haag, haug, hogg, krog, maag, mogg, plog, skog, slog, smog, waag, zogg

5 letters:
-agog, barog, bayog, befog, bihag, blogg, bulog, cosag, craag, dague, defog, delag, dogge, drcog, embog, eqlog, facog, frogg, fseog, gen.g, glogg, graag, grogg, gulag, hilog, hogge, lague, locog, logge, magog, morag, parag, pdogg, phlog, pirog, pogge, progg, recog, rogge, scrog, silog, skrog, smaug, socog, splog, sprog, strog, tague, tofog, wolog, zaugg, zilog

6 letters:
-logue, agogue, analog, anurag, applog, augcog, balrog, bandog, bigdog, buldog, catdog, clague, condog, coydog, croagh, dcslog, dildog, dos/4g, eggnog, epilog, fogdog, frogge, funlog, gaplog, gundog, hamdog, hotdog, ibague, lapdog, medlog, moblog, objlog, parlog, photog, pi-dog, poplog, prague, precog, prelog, prolog, putlog, pyedog, quahog, quohog, ratdog, sawlog, seadog, seahog, sundog, svarog, syslog, tablog, taclog, tetaug, unclog, weblog

7 letters:
-agogue, antifog, antilog, backlog, bairaag, beamdog, belobog, bibliog, bonedog, brewdog, bulldog, calinog, camfrog, caradog, coondog, corndog, datadog, dazhbog, dekalog, demagog, dipolog, eclogue, egg-nog, firedog, graylog, hangdog, hertzog, hirulog, horndog, hot-dog, icefrog, insarag, kenalog, lexicog, lifelog, log-log, longdog, menulog, milblog, monolog, moondog, nidhogg, nig-nog, oceanog, overdog, pedagog, pie-dog, pug-dog, pye-dog, quahaug, roadhog, rsyslog, sandhog, schelog, semilog, sherdog, sinulog, spurdog, starlog, synagog, tagalog, templog, theolog, vandaag, verilog, warblog, wolfdog

8 letters:
abominog, analogue, anti-fog, antismog, armikrog, ballarag, bird-dog, bullfrog, calbayog, chemofog, chilidog, coachdog, dialogue, duologue, epilogue, fire-dog, footslog, freakdog, hang-dog, hedgehog, hop-frog, housedog, isologue, leapfrog, liveblog, madrague, microlog, ortholog, pettifog, portague, q-analog, sheepdog, shockdog, spacehog, swisslog, synagoge, sys-frog, toadfrog, travelog, treefrog, tremadog, underdog, watchdog, waterdog, waterlog, wolf-dog, woodfrog, yon-rogg

9 letters:
bull-frog, bulldogge, catalogue, changelog, cheeselog, chernabog, cs-prolog, decalogue, demagogue, devprayag, flyingdog, glottolog, golliwogg, groundhog, hemagogue, holagogue, homologue, ic-prolog, idealogue, leap-frog, lm-prolog, magalogue, melologue, menagogue, metagogue, microblog, monologue, mummachog, mummichog, nu-prolog, pedagogue, photoblog, qu-prolog, sb-prolog, shot-clog, sinologue, superdawg, synagogue, tree-frog, trialogue, videoblog, whole-hog, wood-frog, zytglogge

10 letters:
astrologue, bandar-log, cholagogue, copenhague, emenagogue, ethnologue, euchologue, haemagogue, hydragogue, hypnagogue, lactagogue, lithagogue, myriologue, mystagogue, ninkharsag, objvprolog, philologue, physagogue, pnu-prolog, porthmadog, sialagogue, swi-prolog, travel-log, travelogue, yellow-dog

11 letters:
brycheiniog, cardiologue, cat-and-dog, dog-eat-dog, ecrc-prolog, electrosmog, emmenagogue, grammalogue, lymphagogue, melanagogue, prairie-dog, psychagogue, psychologue, ptyalagogue, ptysmagogue, rudraprayag, skittle-dog, typedprolog

12 letters:
delta-prolog, galactagogue, isotopologue, magyarorszag, memphremagog, phlegmagogue, secretagogue

13 letters:
beetsterzwaag, modula-prolog, monopolylogue, systemverilog

14 letters:
admiralbulldog, andorra-prolog, antisialagogue, helminthagogue

15 letters:
multi-binprolog, topdog/underdog