The Collaborative International Dictionary of English v.0.48:

paintbrush \paint"brush`\ n.
   A brush used to apply paint.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

paintbrush
    n 1: a brush used as an applicator (to apply paint)

The Free On-line Dictionary of Computing (19 January 2023):

Paintbrush

    A Microsoft Windows tool for creating
   bitmap graphics.

   (1996-08-26)