cowan, n. — Green’s Dictionary of Slang

cowan n.

[ety. unknown; Hotten (1860) offers Gk kuon, a dog (as general pej.) or Scot. cowan or kirwan, a man who builds dry-stone walls without mortar, and thus one who builds but is not a fully qualified mason. Note freemasons’ jargon cowan, one who has not been initiated into the craft]

a sneak, an eavesdropper.

1860		Hotten Dict. of Modern Sl. etc. (2nd edn).
1873		Sl. Dict.