"stout pole," c.1300, "rafter," from Middle Low German or Middle Dutch sparre, from Proto-Germanic *sparron (cf. Old English *spere "spear, lance," Old Norse sperra "rafter, beam"), from PIE root *sper- "spear, pole" (see spear (n.1)). Nautical use dates from 1640. Also borrowed in Old French as esparre, which may have been the direct source of the English word.