| 1 | Latin | irritabilis | irritable, irascible, short-tempered; excitable,... |
| 2 | Latin | irrito | I incite, excite, stimulate, instigate, provoke;... |
| 3 | Latin | irritus | invalid, void, null and void; ineffective,... |
| 4 | Latin | ratus | considered, having been considered; established,... |
| 5 | Latin | rēōr | — |
| 6 | Proto-Italic | rēōr | to reckon, to calculate; to think, to deem, to... |
| 7 | Proto-Indo-European | h₂reh₁- | to think, reason; to arrange |
| 8 | Proto-Indo-European | h₂er- | to fit, to fix, to put together |