- a book size of about 2½ × 4 inches (6 × 10 cm), determined by printing on sheets folded to form 48 leaves or 96 pages. Abbreviation: 48mo, 48°
- a book of this size.
- in forty-eightmo.
Origin of forty-eightmo
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018