lean back vs tilt

lean back is not a noun while tilt is a noun.

Word	Noun	Adjective	Verb	Adverb
lean back	No	No	Yes	No
tilt	Yes	No	Yes	No

As verbs, tilt is a hypernym of lean back; that is, tilt is a word with a broader meaning than lean back:

Other hypernyms of lean back include angle, lean, slant, tip.

lean back (noun)	tilt (noun)
	pitching dangerously to one side
	the property possessed by a line or surface that departs from the vertical
	a slight but noticeable partiality
	a contentious speech act; a dispute where there is strong disagreement
	a combat between two mounted knights tilting against each other with blunted lances

lean back (verb)	tilt (verb)
move the upper body backwards and down	charge with a tilt
	to incline or bend from a vertical position
	heel over
	move sideways or in an unsteady way