blunderbuss n.

mid-13c., from Old English þunor "thunder, thunderclap; the god Thor," from Proto-Germanic *thunraz (source also of Old Norse þorr, Old Frisian thuner, Middle Dutch donre, Dutch donder, Old High German donar, German Donner "thunder"), from PIE *(s)tene- "to resound, thunder" (source also of Sanskrit tanayitnuh "thundering," Persian tundar "thunder," Latin tonare "to thunder"). Swedish tordön is literally "Thor's din." The unetymological -d- also is found in Dutch and Icelandic versions of the word (compare sound (n.1)). Thunder-stick, imagined word used by primitive peoples for "gun," attested from 1904.

"metal sleeve fitted into a machine or hole," 1839, from gerundive of bush (n.) "metal lining of the axle hole of a wheel or touch hole of a gun" (1560s), which is from Middle Dutch busse "box" (cognate with the second element in blunderbuss). Bush-metal "hard brass, gun-metal" is attested from 1847.

"dunce, numbskull," 1620s, from head (n.); the first element is obscure; perhaps from Middle Dutch doner, donder "to thunder" (compare blunderbuss). Dunder also was a native dialectal variant of thunder. In the same sense were dunder-whelp (1620s); dunderpate (1754); dunderpoll (1801).