6 letters:
aceous, acious, tatius

7 letters:
-aceous, -acious

8 letters:
araceous, edacious, glacious, gracious, horatius, ignatius, poaceous, spacious

9 letters:
apiaceous, audacious, bibacious, bodacious, capacious, cepaceous, ceraceous, cetaceous, dicacious, fabaceous, fagaceous, feracious, filaceous, fugacious, fumacious, furacious, julaceous, lilaceous, limaceous, linaceous, lutaceous, meracious, micaceous, minaceous, moraceous, musaceous, nugacious, oleaceous, palacious, pinaceous, pomaceous, rapacious, rosaceous, rudaceous, rutaceous, sagacious, salacious, sebaceous, setaceous, solacious, taxaceous, tenacious, theaceous, tufaceous, ulmaceous, veracious, vexatious, vinaceous, vitaceous, vivacious, volacious, voracious

10 letters:
acanaceous, acinaceous, alliaceous, alutaceous, amylaceous, anonaceous, arenaceous, avenaceous, bardacious, bowdacious, bulbaceous, byssaceous, cactaceous, chylaceous, cistaceous, coriaceous, cornaceous, cretaceous, cretacious, curvaceous, drupaceous, ericaceous, erinaceous, fallacious, foliaceous, gemmaceous, glumaceous, hellacious, herbaceous, ingracious, iridaceous, juncaceous, lamiaceous, lappaceous, lardaceous, lauraceous, lemnaceous, liliaceous, loquacious, malvaceous, marlaceous, meliaceous, mendacious, miniaceous, mordacious, myrtaceous, ochraceous, oleraceous, olivaceous, ostraceous, palmaceous, pancratius, pennaceous, perlaceous, porraceous, predaceous, predacious, priapatius, procacious, pultaceous, rampacious, rubiaceous, sequacious, spinaceous, sporaceous, testaceous, tiliaceous, tophaceous, tuffaceous, umbratious, ungracious, violaceous

11 letters:
alsinaceous, amentaceous, araliaceous, arboraceous, betulaceous, butyraceous, chartaceous, cineraceous, crustaceous, cycadaceous, cyperaceous, disgracious, efficacious, farinaceous, ferulaceous, flirtatious, hederaceous, hordeaceous, linguacious, litigatious, lythraceous, malgracious, menthaceous, mimosaceous, misgracious, onagraceous, ostreaceous, papyraceous, pearlaceous, piperaceous, proteaceous, psittaceous, pyritaceous, resinaceous, rhamnaceous, salicaceous, saponaceous, sapotaceous, scoriaceous, scribacious, scribatious, sepidaceous, shorlaceous, solanaceous, solenaceous, spathaceous, squamaceous, temptatious, truttaceous, unveracious, urticaceous, xyridaceous

12 letters:
acanthaceous, agaricaceous, ampullaceous, apocynaceous, argillaceous, bombacaceous, capillaceous, carbonaceous, cichoraceous, columbaceous, contumacious, corallaceous, corollaceous, dematiaceous, diatomaceous, dipsacaceous, disputatious, furfuraceous, gallinaceous, geraniaceous, graminaceous, lobeliaceous, loganiaceous, lomentaceous, marmoraceous, orchidaceous, ostentatious, oxalidaceous, pandanaceous, pectinaceous, pervicacious, plumulaceous, primulaceous, pulveraceous, ramentaceous, santalaceous, sapindaceous, schistaceous, schorlaceous, scolopaceous, stipulaceous, styracaceous, trepidatious, turbinaceous, verbenaceous

13 letters:
amarantaceous, amygdalaceous, arundinaceous, aurantiaceous, bignoniaceous, boraginaceous, brassicaceous, bromeliaceous, camphoraceous, cinchonaceous, conchylaceous, confervaceous, crassulaceous, cylindraceous, equisetaceous, frumentaceous, gentianaceous, inefficacious, juglandaceous, magnoliaceous, membranaceous, nymphaeaceous, papaveraceous, perspicacious, pilosebaceous, pistillaceous, polygalaceous, polygonaceous, porphyraceous, proteinaceous, sanguinaceous, sarmentaceous, stercoraceous, strobilaceous, subglumaceous

14 letters:
amaranthaceous, anacardiaceous, atramentaceous, balsaminaceous, berberidaceous, campanulaceous, capparidaceous, conchyliaceous, cucurbitaceous, euphorbiaceous, fringillaceous, lycopodiaceous, malpighiaceous, marasritaceous, margaritaceous, molendinaceous, nucamentaceous, nucumentaceous, nyctaginaceous, orobanchaceous, papilionaceous, polemoniaceous, portulacaceous, ranunculaceous, saxifragaceous, simaroubaceous, sterculiaceous, subcrustaceous, unostentatious, valerianaceous, zingiberaceous

15 letters:
amaryllidaceous, asclepiadaceous, caprifoliaceous, chenopodiaceous, convolvulaceous, extrafoliaceous, hamamelidaceous, interfoliaceous, intrafoliaceous, menispermaceous, pergamentaceous, plantaginaceous, plumbaginaceous, supracretaceous, suprafoliaceous, zygophyllaceous

16 letters:
caryophyllaceous

17 letters:
hydrocarbonaceous, scrophulariaceous

19 letters:
argillo-areenaceous, ovate-cylindraceous, ovato-cylindraceous

21 letters:
calcareo-argillaceous

5 letters:
aphis, basis, davis

6 letters:
stasis

7 letters:
devious, tedious, theseus, dreyfus

8 letters:
previous, deviance, dreyfuss

9 letters:
demetrius, obedience, epistasis

10 letters:
prescience, prometheus, obsequious, expedience, cash basis, hypostasis

11 letters:
homogeneous, symphonious, atelectasis

12 letters:
inexpedience, disobedience, rhadamnathus

13 letters:
accrual basis, arteriectasis

14 letters:
bacteriostasis

18 letters:
civil disobedience, on a regular basis

21 letters:
on an irregular basis

22 letters:
on an individual basis