Meaning

verb be careful or certain to do something; make certain of something

verb make certain of

verb protect by insurance

originFirst attested in c. 1440, as a variant of Middle English ensuren (from Anglo-Norman enseurer, itself from Old French en- + seür (“sure”), probably influenced by Old French asseürer (“to assure”)); took on its particular sense of "make safe against loss by payment of premiums" in 1635, replacing assure. Doublet of ensure.

Etymology from Wiktionary, CC BY-SA 3.0