Wiktionary
n. 1 (context uncountable English) a spice mixture that is used to flavor the water in which crabs or other shellfish are boiled 2 a social event in which boiled crabs are featured
Wikipedia
Crab boil usually refers to a spice mixture that is used to flavor the water in which crabs or other shellfish are boiled. But Crab boil can also refer to a social event in which boiled crabs are featured (see seafood boil). Crab boils are known in the Ville Platte areas of Louisiana as "dome lobster boils," stemming from the local term "dome lobster" based on the shape and composition of crabs and their likeness to a domed lobster. The largest of these gatherings is the Crayon d'Orange festival (French for 'Orange Pencil') in Evangeline Parish.
Usage examples of "crab boil".
Next I put in some root beer extract an meat tenderizer an popcorn cheese seasoning an added some blackstrap molasses an crab boil.
The air was hot and salty with the smell of oysters on half shell and Zatarain's Crab Boil.