tetchiness vs irritability

tetchiness and irritability both are nouns.

Word	Noun	Adjective	Verb	Adverb
tetchiness	Yes	No	No	No
irritability	Yes	No	No	No

As nouns, irritability is a hypernym of tetchiness; that is, irritability is a word with a broader meaning than tetchiness:

Other hypernyms of tetchiness include choler, crossness, fretfulness, fussiness, peevishness, petulance.

tetchiness (noun)	irritability (noun)
feeling easily irritated	a disposition to exhibit uncontrolled anger
	excessive sensitivity of an organ or body part
	an irritable petulant feeling