octodecimo /ok-tō-desˈi-mō/

1. Having eighteen leaves to the sheet
2. Contracted 18mo, often read eighteenmo

A book with sheets so folded

• back-combing
• back-combs
• back-country
• backcourt
• backcourts
• back-crawl
• back-cross
• back-crossed
• back-crosses
• back-crossing
• back-date
• back-dated
• back-dates
• back-dating
• back door
• backdoor
• back doors
• back down
• backdown
• back-draught
• back-draughts
• backdrop
• backdrops
• backed
• back-end