Is it ensure, insure, or assure?
"lion-like," late 14c., from Old French leonin or directly from Latin leoninus "belonging to or resembling a lion," from leo (genitive leonis) "lion." Weekley thinks that Leonine verse (1650s), rhymed in the middle as well as the end of the line, probably is from the name of some medieval poet, perhaps Leo, Canon of St. Victor, Paris, 12c.
leonine le·o·nine (lē'ə-nīn)
Of, relating to, or characteristic of a lion.