carboxylic vs carboxyl

carboxylic is not a noun while carboxyl is a noun.

Word	Noun	Adjective	Verb	Adverb
carboxylic	No	Yes	No	No
carboxyl	Yes	Yes	No	No

As adjectives, carboxylic and carboxyl are synonyms defined as:

carboxylic and carboxyl: relating to or containing the carboxyl group or carboxyl radical

carboxylic (noun)	carboxyl (noun)
	the univalent radical -COOH; present in and characteristic of organic acids

carboxylic (adjective)	carboxyl (adjective)
relating to or containing the carboxyl group or carboxyl radical	relating to or containing the carboxyl group or carboxyl radical