Crays, lobsters, prawns, langoustines and their ilk

For the diligent reader, here's some etymological
lore about lobsters, crayfish, prawns, and other
lexicographically challenging but delicious crustaceans.

First, this from AHD3:

Word History: The crayfish, also known as the crawfish, owes its name to a misunderstanding. The actual source of the word may be the Old High German word krebiz, "edible crustacean," or a word related to it. From this Germanic source came Old French crevice, which when taken into English became crevise (first recorded in a document written in 1311-1312). In Old French and Middle English these words designated the crayfish. People began to pronounce and spell the last part of this word as if it were fish, the first fish spelling (actually fysshes) being recorded in 1555. Because of a variation in Anglo-Norman pronunciation, two forms of the word have come down to Modern English: crayfish and crawfish.

Note that the French aren't great at this stuff either, using "langoustines" to refer to both crayfish and prawns, and using both "langouste" and "homard" to refer to the spiny lobster.

Here's clarification of related terms, from a food-related site that includes some recipes

Crayfish are fresh water decapods. Even though they resemble spiny lobsters they are smaller. Close cousins perhaps, but no more. Crayfish in French are ecrivesses. Be there no question but that the best crayfish dishes in the world are served in the state of Louisiana.
Langoustines are closely related to the crayfish but are salt water decapods. Even though the word langoustine is French, it is used in English as well because true langoustines do not exist in North America. One happy bit of news is that recipes calling for crayfish or langoustines can be used interchangeably. The meat of both are delicious, but you will find that crayfish are somewhat lighter and more puffy on the palate and it is that trait that makes them so highly prized throughout France.
To add a bit of confusion, prawns, which are very closely related to shrimps but are not (as is commonly thought) merely "large shrimps" are also called langoustines in French. That is not so much an error (especially on menus) as it is an attempt to give prawns a somewhat higher "status".

Shrimps, which are salt water creatures are called crevettes in French. Some fresh water shrimps also exist but these are not highly prized in the culinary world.
As to lobsters themselves - these salt water creatures come in two general varieties - the spiny lobster (common in France) and the smooth shelled lobster (North America, South Africa, etc). Although smooth shelled lobsters are always called homard in French, the spiny lobster can be referred to as either langouste or homard).

Michael West
Wearing a white sportcoat
and a pink crustacean