sextodecimo

/S EH1 K S T AH0 D EH1 S AH0 M OW0/
noun
  1. 1

    A size of a sheet of paper resulting from folding and cutting a sheet of paper into sixteenths (3.25"-5" x 5"-6.25").

  2. 2

    A book consisting of pages of that size.

Source: https://en.wiktionary.org/wiki/sextodecimo