E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A composing stick is a hand instrument into which a compositor places the letters to be set up. Each row or line of letters is pushed home and held in place by a movable setting rule, against which the thumb presses. When a stick is full, the matter set up is transferred to a galley (q.v.), and from the galley it is transferred to the chase (q.v.). Called a stick because the compositor sticks the letters into it.