early 15c., reclinen, transitive, "cause to lean backward or downwards (on something); lay (something) down," 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 *klein-, suffixed form of root *klei- "to lean"). The intransitive sense of "rest in a recumbent posture" is from 1590s. Related: Reclined; reclining.
Recline is always as strong as lean, and generally stronger, indicating a more completely recumbent position, and approaching lie. [Century Dictionary]
As a companion noun, reclination "action, posture, etc. of reclining" (1570s, from Late Latin reclinationem) seem not to have caught on.