To feague a horse; to put ginger up a horse’s fundament, and formerly, as it is said, a live eel, to make him lively and carry his tail well; it is said, a forfeit is incurred by any horse-dealer’s servant, who shall shew a horse without first feaguing him. Feague is used, figuratively, for encouraging or spiriting one up.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Fawney * FeakNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes