Bible Dictionaries
Octodecimo

Webster's Dictionary

(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.

Bibliography Information
Webster, Noah. Entry for 'Octodecimo'. Noah Webster's American Dictionary. https://www.studylight.org/​dictionaries/​eng/​web/​o/octodecimo.html. 1828.