Green’s Dictionary of Slang

ben n.2

[abbr.]

1. [early 19C–1900s] (orig. theatrical) a benefit, i.e. ‘a theatrical performance the receipts from which are given to a particular actor, the playwright, or some other person connected with the theatre’ (OED).

2. [1900s] benefit.

In phrases

stand ben (v.) [stand v.2 (1) ]

[early 19C] to treat one’s companions at an inn or tavern.