Old English þyddan "to strike, thrust," of imitative origin. Sense of "hit with a dull sound" first recorded 1796. The noun is attested from 1510s.
1. Yet another metasyntactic variable (see foo). It is reported that at CMU from the mid-1970s the canonical series of these was "foo", "bar", "thud", "blat".
2. Rare term for the hash character, "#" (ASCII 35). See ASCII for other synonyms.
[Jargon File]