-MO

a suffix added to the names of certain numerals or to the numerals themselves, to indicate the number of leaves made by folding a sheet of paper; as, sixteenmo or 16mo; eighteenmo or 18mo. it is taken from the latin forms similarly used; as, duodecimo, sextodecimo, ·etc. a small circle, placed after the number and near its top, is often used for -mo; as, 16?, 18?, ·etc.