Definition of octodecimo

< octodecillion

octogenarian >

oc·to·dec·i·mo    (kt-ds-m) KEY 

NOUN:
pl. oc·to·dec·i·mos In both senses also called eighteenmo.

1. The page size, 4 by 6 ¹/₂ inches, of a book composed of printer's sheets folded into 18 leaves or 36 pages.
2. A book composed of octodecimo pages.

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ETYMOLOGY:
Late Latin (in) octdecim, (in) an eighteenth, ablative sing. of octdecimus, eighteenth, from Latin octdecim, eighteen : oct, eight; see okt(u) in Indo-European roots + decem, ten; see dek in Indo-European roots