From Longman Dictionary of Contemporary Englishcrabcrab /kræb/ ●●○ noun 1 
[countable]HB a sea animal with a hard shell, five legs on each side, and two large claws → crustacean2 DF[uncountable] the flesh of this animal that you can cook and eat crab meat dressed crab (=prepared for eating)3 → crabs4 [singular]ANNOY American English informal someone who becomes annoyed easily about unimportant things
[countable]HB a sea animal with a hard shell, five legs on each side, and two large claws → crustacean2 DF[uncountable] the flesh of this animal that you can cook and eat crab meat dressed crab (=prepared for eating)3 → crabs4 [singular]ANNOY American English informal someone who becomes annoyed easily about unimportant thingsExamples from the Corpus
crab• She's such a crab.• Sometimes you can find a Zebra flatworm sharing the snail shell with the hermit crab.• Alaskan king crabs• Form into 10 large crab cakes.• In the confusion, many crabs lose their foothold, tumble into the water and are swept away.• It is fair to warn anglers that thousands of crabs soon make short work of rag and lugworm.• The other crab, rather than being left homeless and therefore extremely vulnerable to predators, instantly jumped into the broken shell.• Not surprisingly, peeler crab is the best hookbait.• I'll have the crab cakes please.• There was less interest in the crabs and squat lobsters, which I claimed as my niche and shared amicably with others.• The fishing was great; you could pick up crabs off the beach.Origin crab 1. Old English crabba2. (1800-1900) crabbed 