| 1 | Ancient Greek | μέτρον | something used to measure: measure, rule, weight;... |
| 2 | Ancient Greek | -τρον | Forms instrument nouns |
| 3 | Proto-Hellenic | -tron | Forms instrument nouns from verb stems |
| 4 | Proto-Indo-European | -trom | Forms nouns denoting a tool or instrument |
| 5 | Proto-Indo-European | -tḗr | Derives agent nouns from verbs, denoting someone... |