When Peruvian authorities refused to send him back to Aruba, he clammed up.
Months later, when I challenged Colonel Boyatt on this highly counterproductive order to his troops, he clammed up on me.
But he clammed up about that, hoping to keep it a secret until he could go back and claim it.
The crack above the door should not be clammed until the muffle begins to get warm.
Kellner had clammed up, and when the now suspicious editor had tried to check Colquhoun's tale personally, Colquhoun had vanished.
clammed means starvation; that is, care killed the cat; for want of food the entrails get "clammed."
bivalve mollusk, c.1500, in clam-shell, originally Scottish, apparently a particular use from Middle English clam "pincers, vice, clamp" (late 14c.), from Old English clamm "bond, fetter, grip, grasp," from Proto-Germanic *klam- "to press or squeeze together" (cf. Old High German klamma "cramp, fetter, constriction," German Klamm "a constriction"). If this is right then the original reference is to the shell. Clam-chowder attested from 1822. To be happy as a clam is from 1833, but the earliest uses do not elaborate on the notion behind it, unless it be self-containment.
"to dig for clams," 1630s, American English, from clam (n.). Clam up "be quiet" is 1916, American English, but clam was used in this sense as an interjection mid-14c.
clam up •The term must be earlier than the date given, although no examples can be provided. Middle English clum, ''be quiet! shut up,'' of obscure origin, may not be related to clam (1916+)