"evergreen tree," 1660s, from spruse (adj.) "made of spruce wood" (early 15c.), literally "from Prussia," from Spruce, Sprws (late 14c.), unexplained alterations of Pruce "Prussia," from an Old French form of Prussia. Spruce seems to have been a generic term for commodities brought to England by Hanseatic merchants (beer, board, leather, see spruce (v.)), and the tree was believed to have come from Prussia.
1590s, from the adjective meaning "to make trim or neat," from spruce leather (mid-15c., see spruce (n.)), which was used to make a popular style of jerkins in the 1400s that was considered smart-looking.