clam [OE] It is not easy to prise apart a clam, and this tight grip lies behind the origin of the word. Clam in Old English originally meant ‘a bond, something that holds tight’ and then ‘a clamp’ [LME], and probably had the same source as clamp [ME]. There is also an English dialect word clam [LME], meaning ‘to be sticky or to stick to something’, which is related to clay [OE]. It is also where clammy [LME]—originally spelled claymy—comes from. As a name of the shellfish the word appears in the early 16th century. To clam up, ‘shut up’, is recorded from America from the early 20th century and linked to the shellfish, but there is one single example of clam from c.1350 which appears to have the same meaning and which has been linked to the ‘sticky’ sense. See also happy.