lean vs underweight

lean is a noun but underweight is not a noun.

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

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

lean (adjective)	underweight (adjective)
lacking in mineral content or combustible material	being very thin
lacking excess flesh
not profitable or prosperous
containing little excess

lean (verb)	underweight (verb)
rely 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