Used of damage, harm, loss, or a break in a relationship that is so bad it can never be repaired or put right. It is the everyday partner of 'repair', but notice how differently the two behave: you repair a bike, yet almost nobody says 'irreparable bike'. This word sticks to a small set of nouns — irreparable damage, irreparable harm, irreparable loss, irreparable injury, an irreparable rift or breakdown. It is formal but not rare; you meet it in newspapers, in law (courts speak of 'irreparable harm' as a test for granting an emergency order), and in serious speech. One more thing about the sound: the stress falls on the second syllable, ir-REP-ar-able, not on 'repair' — so it does not sound like the verb inside it, which surprises people. There is a rarer pronunciation with 'repair' in it, but the standard one is the first.