complimentary vs gratuitous

complimentary and gratuitous both are adjectives.

Word	Noun	Adjective	Verb	Adverb
complimentary	No	Yes	No	No
gratuitous	No	Yes	No	No

As adjectives, complimentary and gratuitous are synonyms defined as:

Other synonyms of complimentary include costless, free, gratis.

complimentary (adjective)	gratuitous (adjective)
conveying or resembling a compliment	without cause
costing nothing	unnecessary and unwarranted
	costing nothing