tailcoat vs dress suit

tailcoat and dress suit both are nouns.

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

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

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

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

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