decimosexto

from The Century Dictionary.

• noun See sextodecimo.

from the GNU version of the Collaborative International Dictionary of English.

• noun 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°.
• adjective Having sixteen leaves to a sheet.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Having sixteen leaves to a sheet.