[doo-uh-des-uh-moh, dyoo-]

noun, plural du·o·dec·i·mos.

Also called twelvemo. a book size of about 5 × 7½ inches (13 × 19 cm), determined by printing on sheets folded to form 12 leaves or 24 pages. Symbol: 12 mo, 12°
a book of this size.


in duodecimo; twelvemo.

Origin of duodecimo

1650–60; short for Latin in duodecimō in twelfth
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

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noun plural -mos

Also called: twelvemo a book size resulting from folding a sheet of paper into twelve leavesOften written: 12mo, 12°
a book of this size

Word Origin for duodecimo

C17: from Latin phrase in duodecimō in twelfth, from duodecim twelve
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for duodecimo

1650s, from Latin in duodecimo (folded) "in a twelfth" of a sheet, from ablative of duodecimus "twelfth," from duodecim (see dozen). Often abbreviated 12mo.; a book in which each page is the twelfth part of the printer's sheet.

Online Etymology Dictionary, © 2010 Douglas Harper