sarcasm vs irony

sarcasm and irony both are nouns.

Word	Noun	Adjective	Verb	Adverb
sarcasm	Yes	No	No	No
irony	Yes	No	No	No

As nouns, sarcasm and irony are synonyms defined as:

Other synonyms of sarcasm include caustic remark, satire.

sarcasm (noun)	irony (noun)
witty language used to convey insults or scorn	incongruity between what might be expected and what actually occurs
	a trope that involves incongruity between what is expected and what occurs
	witty language used to convey insults or scorn