sixteenmo

UK: /ˈsɪksˈtiːnməʊ/ US: (siks′tēn′mō)

WordReference Random House Unabridged Dictionary of American English © 2026

six•teen•mo  (siks′tēn′mō), n., pl. -mos, adj. 
n. 

1. Printing Also called sextodecimo. a book size (about 4×6 in.;
   10×15 cm) determined by printing on sheets folded to form 16 leaves or 32 pages.
2. Printing a book of this size. Symbol: 16mo, 16°

adj. 

3. Printing printed, folded, or bound in sixteenmo;
   sextodecimo.

• sixteen + -mo 1840–50

Collins Concise English Dictionary © HarperCollins Publishers::

sixteenmo / ˈsɪksˈtiːnməʊ/ noun ( -mos)

1. Also called: sextodecimo a book size resulting from folding a sheet of paper into 16 leaves or 32 pages, each one sixteenth the size of the sheet
   Often written: 16mo, 16°