mid-13c., "act or action of securing, uniting, etc.," verbal noun from bind (v.). Meaning "thing that binds" is from c. 1300; "state of being bound" is from late 14c. Meaning "covering of a book" is recorded from 1640s.
late 14c., "serving to bind," past-participle adjective from bind (v.). Meaning "having power to bind" is from 1610s.
the book had a leather binding
a binding contract