| 1 | English | ruler | A , flat, rectangular measuring or drawing device... |
| 2 | Middle English | reuler | ruler, leader, governor; ruler |
| 3 | Middle English | reule | legal code, set of rules; moral code, principles;... |
| 4 | Old French | reule | rule; ruler; rule |
| 5 | Latin | rēgula | — |
| 6 | Latin | -ula | regō + API → rēgula; tegō + API → tēgula;... |
| 7 | Proto-Indo-European | -tlom | Alternative form of *-trom |
| 8 | Proto-Indo-European | -trom | Forms nouns denoting a tool or instrument |
| 9 | Proto-Indo-European | -tḗr | Derives agent nouns from verbs, denoting someone... |