- Decimosexto Dec`i*mo*sex"to, n. [Prop., in sixteenth; fr. L. decimus tenth + sextus sixth.] A book consisting of sheets, each of which is folded into sixteen leaves; hence, indicating, more or less definitely, a size of book; -- usually written 16mo or 16[deg]. [1913 Webster]
The Collaborative International Dictionary of English. 2000.