Definition of "casky"

[…] laid handsomely out with such a rattler on the nose as nobody could have expected from a casky little man of five-feet-nothing.

Alexander Montgomery, Five-Skull Island And Other Tales of the Malay Archipelago

[…] a rancid flavor, or one of rubber, plastic material, hydrocarbons, or a casky taste.

1996, Emile Peynaud, Jacques Blouin, The Taste of Wine: The Art Science of Wine Appreciation, page 287