full dress vs dress suit

full dress and dress suit both are nouns.

Word	Noun	Adjective	Verb	Adverb
full dress	Yes	No	No	No
dress suit	Yes	No	No	No

As nouns, full dress and dress suit are synonyms defined as:

full dress and dress suit: formalwear consisting of full evening dress for men

Other synonyms of full dress include tail coat, tailcoat, tails, white tie, white tie and tails.

full dress (noun)	dress suit (noun)
formalwear consisting of full evening dress for men	formalwear consisting of full evening dress for men