1630s, a tool for winding the spring of a wheel-lock firearm, from German Spanner, from spannen "to join, fasten, extend, connect," from Proto-Germanic *spannan, from PIE root *(s)pen- "to draw, stretch, spin" (source also of spin (v.)). Meaning "wrench" is from 1790. Figurative phrase spanner in the works attested from 1921 (Wodehouse).
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