mo

mo is an Adverb

Definition:

[1] More; -- usually, more in number. [Obs.] An hundred thousand mo. Chaucer. Likely to find mo to commend than to imitate it. Fuller.

[2] 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.