DUODECIMO a. 2 definitions
Having twelve leaves to a sheet; as, a duodecimo from, book, leaf, size, etc.
MO a.
xteenmo 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.