Is it ensure, insure, or assure?
Old English freo "free, exempt from, not in bondage," also "noble; joyful," from Proto-Germanic *frijaz (cf. Old Frisian fri, Old Saxon and Old High German vri, German frei, Dutch vrij, Gothic freis "free"), from PIE *prijos "dear, beloved," from root *pri- "to love" (cf. Sanskrit priyah "own, dear, beloved," priyate "loves;" Old Church Slavonic prijati "to help," prijatelji "friend;" Welsh rhydd "free").
The primary sense seems to have been "beloved, friend, to love;" which in some languages (notably Germanic and Celtic) developed also a sense of "free," perhaps from the terms "beloved" or "friend" being applied to the free members of one's clan (as opposed to slaves, cf. Latin liberi, meaning both "free" and "children").
Cf. Gothic frijon "to love;" Old English freod "affection, friendship," friga "love," friðu "peace;" Old Norse friðr, German Friede "peace;" Old English freo "wife;" Old Norse Frigg "wife of Odin," literally "beloved" or "loving;" Middle Low German vrien "to take to wife, Dutch vrijen, German freien "to woo."
Of nations, "not subject to foreign rule or to despotism," it is recorded from late 14c. (Free world "non-communist nations" attested from 1950.) Sense of "given without cost" is 1580s, from notion of "free of cost." Free lunch, originally offered in bars to draw in business, by 1850, American English. Free pass on railways, etc., attested by 1850. Free speech in Britain used of a privilege in Parliament since the time of Henry VIII. In U.S., as a civil right, it became a prominent phrase in the debates over the Gag Rule (1836).
Free enterprise recorded from 1890; free trade is from 1823. Free will is from early 13c. Free association in psychology is from 1899. Free love "sexual liberation" attested from 1822. Free range (adj.) is attested by 1960. Free and easy "unrestrained" is from 1690s.
Old English freogan "to free, liberate, manumit," also "to love, think of lovingly, honor," from freo (see free (adj.)). Cf. Old Frisian fria "to make free;" Old Saxon friohan "to court, woo;" German befreien "to free," freien "to woo;" Old Norse frja "to love;" Gothic frijon "to love." Related: Freed; freeing.
Without charge; gratis; free gratis: They gave him a sandwich absolutely for free
[1940s+; based on Yiddish far gornisht, ''for nothing'']
Said of a capability of a programming language or hardware equipment that is available by its design without needing cleverness to implement: "In APL, we get the matrix operations for free." "And owing to the way revisions are stored in this system, you get revision trees for free." The term usually refers to a serendipitous feature of doing things a certain way (compare big win), but it may refer to an intentional but secondary feature.