Called a fish out of the coop by those friars who wished to evade the Friday fast by eating chickens instead of fish. (See Yarmouth.)
(A). A castrated cock.
We also sometimes hear of a Glasgow capon, a salt herring.
(A). A love-letter. In French, poulet means not only a chicken but also a love-letter, or a sheet of note-paper. Thus Henri IV., consulting with Sully about his marriage, says: “My niece of Guise would please me best, though report says maliciously that she loves poulets in paper better than in a fricasee.”
“Boyet ... break up this capon [i.e. open this love-letter].” —Shakespeare. Love's Labour's Lost, iv. 1.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894