I. clam 1 /klæm/ BrE AmE noun [countable]
[ Date: 1500-1600 ; Origin: clam 'two-part fastener' (14-20 centuries) , from Old English clamm 'chain, rope, etc. for tying something up' ; from the tight shutting of a clam shell ]
1 . a ↑ shellfish you can eat that has a shell in two parts that open up:
clam chowder (=a type of soup)
2 . as happy as a clam American English informal very happy
3 . American English informal someone who does not say what they are thinking or feeling
II. clam 2 BrE AmE verb ( past tense and past participle clammed , present participle clamming )
clam up phrasal verb
informal to suddenly stop talking, especially when you are nervous or shy:
A sensitive child is likely just to clam up.