also headbutt, 1935, from head (n.) + butt (n.5). As a verb, by 1946. Related: Head-butting (1917 as a noun).
"thick end," 1580s," from butt (n.1) + end (n.). Meaning "the mere end," without regard to thickness, is from 1590s.
"joint formed by welding," 1831, from weld (v.).