1. (a.) Having eighteen leaves to a sheet; as, an octodecimo form, book, leaf, size, etc.
2. (n.) A book composed of sheets each of which is folded into eighteen leaves; hence; indicating more or less definitely a size of book, whose sheets are so folded; -- usually written 18mo or 18, and called eighteenmo.
Thesaurus Entries
Her Highness, Her Majesty, His Majesty, O, Old Mug, achievement, acme, aggrandize, alerion, all, animal charge, anklet, annular muscle, annulet, annulus, anoint, apex, apogee, apotheose, apotheosize, areola, argent, armlet, armorial bearings, armory, arms, aureole, authority, azure, baby tooth, bandeau, bangle, bar, bar sinister, baton, bawbee, bays, beads, bean, bearings, beatify, bend, bend sinister, bicuspid, bijou, billet, blanket, blazon, blazonry, bonnet, bordure, bracelet, bracket capital, breastpin, broad arrow, brooch, brow, bucktooth, button up, cadency mark, canine, canonize, canton, cap, cap of dignity, cap of maintenance, capital, capsheaf, capstone, caput, carry to completion, ceil, ceiling, ceiling fixture, chain, chair, chandelier, chaplet, charge, charm, chatelaine, chevron, chief, circle, circlet, circuit, circumference, circus, cite, civic crown, clean up, climax, close out, close up, closed circle, cloud nine, coat of arms, cockatrice, coif, coin, complete, conclude, consummate, copestone, cork, cornice, corona, corona lucis, coronal, coronet, crescent, crest, cross, cross moline, crown with laurel, culmen, culminate, culmination, cup, cuspid, cutter, cycle, deciduous tooth, decorate, deify, dent, denticle, denticulation, dentil, dentition, develop, device, diadem, difference, differencing, discus, disk, do honor, do to perfection, dogtooth, dollar, dome, dominion, double eagle, doubloon, ducat, duodecimo, eagle, earring, edge, eighteenmo, electrolier, elevate, emperor, empress, end, ennoble, enshrine, enthrone, ermine, ermines, erminites, erminois, escutcheon, eternal return, exalt, extreme, extreme limit, extremity, eyetooth, fairy ring, falcon, fang, farthing, fess, fess point, field, file, fillet, final stroke, final touch, finalize, finish, finish off, finish up, finisher, finishing stroke, five-dollar gold piece, fiver, flanch, fleur-de-lis, florin, fob, folio, fore tooth, fourpence, fourpenny, fret, frost, fur, fusil, gagtooth, gang tooth, garland, gasolier, gem, get done, get it over, get through, get through with, glamorize, glorify, glory, gold piece, gold tooth, government, great seal, griffin, grinder, groat, guinea, gules, gyron, half crown, half dollar, half eagle, halfpenny, halo, hard money, hat, hatchment, head, heading, headpiece, heaven, heavens, height, helmet, heraldic device, high noon, highest degree, highest pitch, highest point, honor, honor point, hood, ice, immortalize, impalement, impaling, imperial, improve, inaugurate, incisor
