ir-
Makes words opposite
Ir- is a prefix meaning "not," attached to words beginning with r: irresponsible, irrelevant, irregular, irresistible.
It's a variant of in- that evolved because saying "inresponsible" is awkward—the sounds flow better when the prefix matches the following consonant.
The same pattern gives us il- before l (illegal) and im- before m or p (immoral, improper).
Deviating from normal patterns
- irresponsibleLacking sense of duty
- irrelevantNot pertinent
- irrationalLacking sound judgment
- irreversibleCannot be undone
irresistible · irreconcilable · irreplaceable · irrefutable · irrevocable · irreparable · irrepressible · irredeemable
Exposure to radiant energy
- irrigationArtificial water supply for agriculture
- irrigateSupply land with water
- iritisColored-ring inflammation
- irritationMild anger or inflammation
irritable · irritant · irradiate · irrigator · irritability · irradiance
irregular
Deviating from normal patterns
- irresponsibleLacking sense of duty
- irrelevantNot pertinent
- irrationalLacking sound judgment
irreversible · irresistible · irreconcilable · irreplaceable · irrefutable · irrevocable · irreparable · irrepressible · irredeemable · irremovable
irradiation
Exposure to radiant energy
- irrigationArtificial water supply for agriculture
- irrigateSupply land with water
- iritisColored-ring inflammation
irritation · irritable · irritant · irradiate · irrigator · irritability · irradiance