Duodecimo
Duodecimo , adjective
[Latin in duodecimo in twelfth, from duodecimus twelfth, fr. duodecim twelve. See Dozen.]
Having twelve leaves to a sheet; as, a duodecimo from, book, leaf, size, etc.
Duodecimo ({not transcribed}) , noun
A book consisting of sheets each of which is folded into twelve leaves; hence, indicating, more or less definitely, a size of a book; -- usually written 12mo or 12°.