Is it ensure, insure, or assure?
mid-13c., "income;" c.1300, "benefit, advantage;"from Old French prufit, porfit "profit, gain" (mid-12c.), from Latin profectus "profit, advance, increase, success, progress," noun use of past participle of proficere (see proficiency). As the opposite of loss, it replaced Old English gewinn. Profit margin attested from 1853.
early 14c., "to advance, benefit, gain," from profit (n.) and from Old French prufiter, porfiter "to benefit," from prufit (see profit (n.)). Related: Profited; profiting.