lean vs lean against

lean is a noun but lean against is not a noun.

Word	Noun	Adjective	Verb	Adverb
lean	Yes	Yes	Yes	No
lean against	No	No	Yes	No

lean (noun)	lean against (noun)
the property possessed by a line or surface that departs from the vertical

lean (adjective)	lean against (adjective)
lacking in mineral content or combustible material
lacking excess flesh
not profitable or prosperous
containing little excess

lean (verb)	lean against (verb)
rely on for support	rest on for support
cause to lean or incline
to incline or bend from a vertical position
cause to lean to the side
have a tendency or disposition to do or be something; be inclined