Green’s Dictionary of Slang

1. (prizefighting) a heavy blow that makes the recipient reel.

1842

Whip & Satirist of NY & Brooklyn (NY) 3 Sept. n.p.: Jim stopped him by giving him a reeler on his ‘dice box’.

2. (Aus.) a drunkard (who reels around).

1895

C. Crowe Aus. Sl. Dict. 13: Butted a Reeler, met a drunken man.