To cheat, to obtain goods and decamp without paying for them.
“The landlord explained it by saying that `a bilk' is a man who never misses a meal and never pays a cent.” —A. K. McClure: Rocky Mountains letter xxii. p. 211.
To “bilk” in cribbage is to spoil your adversaries' score; to balk him. Perhaps the two words are mere variants.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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