Is it ensure, insure, or assure?
1902, from French, literally "free verse," lines of varying length.
I remarked some years ago, in speaking of vers libre, that 'no vers is libre for the man who wants to do a good job.' The term, which fifty years ago had an exact meaning in relation to the French alexandrine, now means too much to mean anything at all. [T.S. Eliot, introduction to "Selected Poems of Ezra Pound," 1928]
(French: "free verse"), 19th-century poetic innovation that liberated French poetry from its traditional prosodic rules. In vers libre, the basic metrical unit is the phrase rather than a line of a fixed number of syllables, as was traditional in French versification since the Middle Ages. In vers libre, the lengths of lines may vary according to the sense of the poem, the complete sentence replaces the stanza as a unit of meaning, and rhyme is optional