first-class vs splendid

first-class and splendid both are adjectives.

Word	Noun	Adjective	Verb	Adverb
first-class	No	Yes	No	No
splendid	No	Yes	No	No

As adjectives, first-class and splendid are synonyms defined as:

Other synonyms of first-class include excellent, fantabulous, mean, ripping.

first-class (adjective)	splendid (adjective)
very good; of the highest quality	having great beauty and splendor
	characterized by grandeur
	very good; of the highest quality