1. a person or thing that binds.
2. a detachable cover, resembling the cover of a notebook or book, with clasps or rings for holding loose papers together: a three-ring binder.
3. a person who binds books; a bookbinder.
6. Chemistry. any substance that causes the components of a mixture to cohere.
7. Painting. a vehicle in which pigment is suspended.
8. (in powder metallurgy) a substance for holding compacted metal powder together while it is being sintered.
9. Building Trades.
a. a stone, as a perpend, for bonding masonry.
b. a girder supporting the ends of two sets of floor joists.
c. a material for holding loose material together, as in a macadamized road.