white tie vs tailcoat

white tie and tailcoat both are nouns.

Word	Noun	Adjective	Verb	Adverb
white tie	Yes	No	No	No
tailcoat	Yes	No	No	No

As nouns, white tie and tailcoat are synonyms defined as:

white tie and tailcoat: formalwear consisting of full evening dress for men

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

white tie (noun)	tailcoat (noun)
bow tie worn as part of a man's formal evening dress	formalwear consisting of full evening dress for men
formalwear consisting of full evening dress for men