• clam •
Pronunciation: klæm • Hear it!
Part of Speech: Noun
Meaning: : 1. An edible, burrowing bivalve mollusk of the class Pelecypoda, found in the sand under fresh and salt water. 2. a clamp or vise. 3. (Slang) A dollar. 4. (Verb: "to clam up") To seal one's lips, to refuse to talk.
Notes: 
It is easy to see how the relation with clamp could be confused with clam. With this in mind, the idiom "to clam up" arose: to clamp one's lips closed the way a clam clamps its two shells together for protection. The use of "clam" to refer to dollars in the US (50 clams = $50) is easy to follow if you know that Indian wampum (money) was a string of shells. But why would anyone be as happy as a clam? Have you ever seen a clam smile? The full original phrase was "happy as a clam at high tide", the only time when the little critters are safe from hungry animals.
In Play: As you can see already, today's word is a favorite of English speakers and has many colloquial uses, "When we asked the kids who had tracked mud across the kitchen floor, they all clammed up." Using this word to refer to dollars is very slangy but has its humorous uses, "Emma Chiset must have paid 500 clams for that gown she wore to the Fly Ball last weekend."
Word History: Today's word comes from Old English clamm "a bond, clamp", which points to an Old Germanic form klam- "to press or squeeze together". This root ended up in English as clam, clamp and, probably, cramp. It is possible that climb in the sense of "cling", as 'a climbing vine', may have originated in the same root. Clammy "wet, sticky," on the other hand, had a different origin. It was widely spelled claymy in the 15th century, but clam was used to refer to clay at about the same time. In any event, although we associate the adjective with clams now, the original association was with clay.
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