bony vs underweight

bony and underweight both are adjectives.

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

As adjectives, bony and underweight are synonyms defined as:

Other synonyms of bony include boney, scraggly, scraggy, scrawny, skinny, weedy.

bony (adjective)	underweight (adjective)
having bones especially many or prominent bones	being very thin
composed of or containing bone
being very thin