Learn English – Etymology of “French fries”

According to this paper (PDF) from Phillip Slavin, chicken was one meat that even the peasantry could afford to eat.

Although poultry occupied the smallest part of demesne livestock, constituting about two per cent of it (Table 1), its social importance and omnipresence cannot be understated, despite scholarly marginalization. Chicken meat constituted an important part of everyday diet, and it was afforded by virtually every social stratum both in England and the Continent

Since eating it wasn't reserved to rich French-speaking folk, it makes sense that the word for it as food wasn't either.

As another answer also pointed out, the word poultry came into the language from Old Norman (presumably with the Conquest).

So, given a social situation where everyone was eating chicken but only Old English speakers were raising them, it makes sense that we ended up with two words for it as food, and one (Old English-derived) word for it as an animal.

I'd call such a packaged (typically derogatory) name an epithet.

Merriam-Webster's definition of epithet:

A word or phrase that describes a person or thing

An offensive word or name that is used as a way of abusing or insulting someone

From Wikipedia's article on epithet:

An epithet, is a byname or a descriptive term (word or phrase), accompanying or occurring in place of a name and having entered common usage. It can be described as a glorified ... In contemporary usage, epithet often refers to an abusive, defamatory, or derogatory phrase, such as a racial epithet.

From Robert A. Harris' "Handbook of Rhetorical Devices" (page 6)

Epithet is an adjective or adjective phrase appropriately qualifying a subject (noun) by naming a key or important characteristic of the subject, as in "laughing happiness," "sneering contempt," "untroubled sleep," "peaceful dawn," and "lifegiving water." Sometimes a metaphorical epithet will be good to use, as in "lazy road," "tired landscape," "smirking billboards," "anxious apple." Aptness and brilliant effectiveness are the key considerations in choosing epithets. Be fresh, seek striking images, pay attention to connotative value.

A transferred epithet is an adjective modifying a noun which it does not normally modify, but which makes figurative sense:

At length I heard a ragged noise and mirth of thieves and murderers .... --George Herbert

Blind mouths! that scarce themselves know how to hold / A sheep hook ... --John Milton

In an age of pressurized happiness, we sometimes grow insensitive to subtle joys.

The striking and unusual quality of the transferred epithet calls attention to it, and it can therefore be used to introduce emphatically an idea you plan to develop. The phrase will stay with the reader, so there is no need to repeat it, for that would make it too obviously rhetorical and even a little annoying. Thus, if you introduce the phrase, "diluted electricity," your subsequent development ought to return to more mundane synonyms, such as "low voltage," "brownouts," and so forth. It may be best to save your transferred epithet for a space near the conclusion of the discussion where it will be not only clearer (as a synonym for previously stated and clearly understandable terms) but more effective, as a kind of final, quintessential, and yet novel conceptualization of the issue. The reader will love it.