Is it ensure, insure, or assure?
1705, from Latin recumbentem (nominative recumbens), present participle of recumbere "recline, lie down, lie down again;" of things, "to fall, sink down, settle down," from re- "back" (see re-) + -cumbere "to lie down" (see succumb). Related: Recumbency (1640s). A verb, recumb, has been attempted in English occasionally since 1670s.
recumbent re·cum·bent (rĭ-kŭm'bənt)
Lying down, especially in a position of comfort; reclining.