Is it ensure, insure, or assure?
Old English hamor "hammer," from Proto-Germanic *hamaraz (cf. Old Saxon hamur, Middle Dutch, Dutch hamer, Old High German hamar, German Hammer. The Old Norse cognate hamarr meant "stone, crag" (it's common in English place names), and suggests an original sense of "tool with a stone head," from PIE *akmen "stone, sharp stone used as a tool" (cf. Old Church Slavonic kamy, Russian kameni "stone"), from root *ak- "sharp" (see acme). Hammer and sickle as an emblem of Soviet communism attested from 1921, symbolizing industrial and agricultural labor.
late 14c., from hammer (n.). Meaning "to work (something) out laboriously" recorded from 1580s. Meaning "to defeat heavily" is from 1948. Related: Hammered; hammering. Hammered as a slang synonym for "drunk" attested by 1986.
hammer ham·mer (hām'ər)
(1.) Heb. pattish, used by gold-beaters (Isa. 41:7) and by quarry-men (Jer. 23:29). Metaphorically of Babylon (Jer. 50:23) or Nebuchadnezzar. (2.) Heb. makabah, a stone-cutter's mallet (1 Kings 6:7), or of any workman (Judg. 4:21; Isa. 44:12). (3.) Heb. halmuth, a poetical word for a workman's hammer, found only in Judg. 5:26, where it denotes the mallet with which the pins of the tent of the nomad are driven into the ground. (4.) Heb. mappets, rendered "battle-axe" in Jer. 51:20. This was properly a "mace," which is thus described by Rawlinson: "The Assyrian mace was a short, thin weapon, and must either have been made of a very tough wood or (and this is more probable) of metal. It had an ornamented head, which was sometimes very beautifully modelled, and generally a strap or string at the lower end by which it could be grasped with greater firmness."