WordWeight : Weighing the Words

Pronunciation : -mo.
Definition : Defn: 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.
Source : Webster's Unabridged Dictionary, 1913