crookback vs gibbous

crookback is a noun but gibbous is not a noun.

Word	Noun	Adjective	Verb	Adverb
crookback	Yes	Yes	No	No
gibbous	No	Yes	No	No

As adjectives, crookback and gibbous are synonyms defined as:

crookback and gibbous: characteristic of or suffering from kyphosis, an abnormality of the vertebral column

Other synonyms of crookback include crookbacked, humpbacked, humped, hunchbacked, kyphotic.

crookback (noun)	gibbous (noun)
a person whose back is hunched because of abnormal curvature of the upper spine

crookback (adjective)	gibbous (adjective)
characteristic of or suffering from kyphosis, an abnormality of the vertebral column	(used of the moon) more than half full
	characteristic of or suffering from kyphosis, an abnormality of the vertebral column