Yours, Etc.: Origins and Uses of 8 Sign-Offs
"leaning forward," 1660s, from Latin procumbentem (nominative procumbens), present participle of procumbere "to fall forward, fall prostrate," from pro "forward" (see pro-) + -cumbere "to lie down" (see succumb). Related: Procumbently.
procumbent pro·cum·bent (prō-kŭm'bənt)adj. Lying face down; prone.