Octavo, ok-tā′vō, adj. having eight leaves to the sheet.—n. a book printed on sheets folded into eight leaves, contracted 8vo—usually meaning a medium octavo, 6×9½ inches. Smaller octavos are—post 8vo, 5½×8½ in.; demy 8vo, 5¼×8 in.; crown 8vo, 5×7½ in.; cap 8vo, 4½×7 in. Larger octavos are—royal 8vo, 6½×10 in.; super-royal 8vo, 7×11 in.; imperial 8vo, 8¼×11 in.:—pl. Octā′vos.
Octennial, ok-ten′i-al, adj. happening every eighth year: lasting eight years.—adv. Octenn′ially.—n. Octocen′tenary, the 800th anniversary of an event. [L. octennis—octo, eight, annus, a year.]
Octillion, ok-til′yun, n. the number produced by raising a million to the eighth power, expressed by a unit with forty-eight ciphers: in France and the United States, one thousand raised to the ninth power, expressed by a unit with twenty-seven ciphers. [L. octo, eight, million.]
October, ok-tō′bėr, n. the eighth month of the Roman year, which began in March: the tenth month in our calendar. [L. octo, eight.]
Octobrachiate, ok-tō-brā′ki-āt, adj. having eight brachia, arms, or rays.
Octocerous, ok-tos′e-rus, adj. having eight arms or rays.
Octodecimo, ok-tō-des′i-mō, adj. having eighteen leaves to the sheet, contracted 18mo.—adj. Octodec′imal (crystal.), having eighteen faces. [L. octodecim, eighteen—octo, eight, decem, ten.]
Octodentate, ok-tō-den′tāt, adj. having eight teeth.
Octofid, ok′tō-fid, adj. (bot.) cleft into eight segments.
Octogenarian, ok-tō-je-nā′ri-an, n. and adj. one who is eighty years old, or between eighty and ninety.—adj. Octog′enary.