from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. The page size, 4 by 6 1/2 inches, of a book composed of printer's sheets folded into 18 leaves or 36 pages.
  • n. A book composed of octodecimo pages.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. A size of a sheet of paper resulting from folding and cutting a sheet of paper into eighteenths (3.5"-4.5" x 4.9"-5.9").
  • n. A book consisting of pages of that size.

from the GNU version of the Collaborative International Dictionary of English

  • adj. Having eighteen leaves to a sheet
  • n. A book composed of sheets each of which is folded into eighteen leaves; hence; indicating more or less definitely a size of book, whose sheets are so folded; -- usually written 18mo or 18°, and called eighteenmo.

from The Century Dictionary and Cyclopedia

  • n. Same as eighteenmo. Abbreviated 18mo.


Late Latin (in) octōdecimō, (in) an eighteenth, ablative sing. of octōdecimus, eighteenth, from Latin octōdecim, eighteen : octō, eight; see oktō(u) in Indo-European roots + decem, ten; see dekm̥ in Indo-European roots.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From Latin ablative of octusdecimus ("eighteenth") (Wiktionary)


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  • Ooh! I'm going to list arsenal.

    February 21, 2007

  • It's not significant to a whole lot of people, c_b. But it *is* a damn fun word to have in one's arsenal.

    February 21, 2007

  • Cool word! I'm not going to list it myself, though, because it's not that significant to me. ;) Just you wait until I have a list it will fit on, like 10-letter words that begin and end with the same letter. Or something like that.

    February 21, 2007

  • A book composed of sheets folded into 18 leaves (36 pages), usually called 18mo. Page size is about 4 by 6 1/2 inches.

    February 21, 2007