From the OED: Brick... 6. slang or colloquial. As predicate: a person regarded as decent, generous, helpful, or reliable. Probably with reference to the person's perceived solidity and dependability. Now somewhat dated...1845 I don't stick To declare Father Dick..was a ‘Regular Brick’.?...1860 I think you're a brick to do that, Johnny Green...1936 She's a brick, too, Sewell! I never thought Ann Lovelace could be so true a friend as she's shown herself to me.