Is it ensure, insure, or assure?
early 15c., from Old French recliner "rest, lay; bend, lean over" (13c.) and directly from Latin reclinare "to bend back, to lean back; cause to lean," from re- "back, against" (see re-) + clinare "to bend," from PIE *klei-n-, suffixed form of *klei "to lean" (see lean (v.)). Related: Reclined; reclining.
Recline is always as strong as lean, and generally stronger, indicating a more completely recumbent position, and approaching lie. [Century Dictionary]