OCTAVO'S fits the letter count and definition,
oc•ta•vo (ɒkˈteɪ voʊ, -ˈtɑ-)
n., pl. -vos,
adj. n.
1. a book size of about 6 x 9 in. (16 x 23 cm), determined by printing on sheets folded to form 8 leaves or 16 pages. Symbol: 8vo, 8°
2. a book of this size.
... but I have no idea if it's the correct answer and, if it is, how the rest of the clue works - are these cryptic clues?