Common Words:
* Irresponsible: Not responsible or reliable.
* Irregular: Not regular or consistent.
* Irrelevant: Not relevant or important.
* Irreplaceable: Impossible to replace.
* Irreversible: Impossible to reverse or undo.
* Irritable: Easily annoyed or angered.
* Irrational: Not logical or reasonable.
* Irresistible: Impossible to resist.
Less Common Words:
* Irreconcilable: Impossible to reconcile or bring together.
* Irreducible: Impossible to reduce or simplify.
* Irrecoverable: Impossible to recover or regain.
* Irrefutable: Impossible to refute or disprove.
* Irregardless: (Incorrect usage) A non-standard word often used instead of "regardless."
* Irrevocable: Impossible to revoke or cancel.
* Irradiate: To expose to radiation.
* Irrigate: To supply water to land for agriculture.
* Irrupt: To burst in or out suddenly.
* Irruption: A sudden burst or influx.
Note: The prefix "irr-" generally indicates negation or opposition to the following root word.