*-þrą

From Proto-Indo-European *-tro-m, the neuter thematic form of an instrument-noun suffix. It belongs to the wider PIE instrument-suffix family *-tro-,*-tlo-,*-dʰro-,*-dʰlo-, which Ringe (2017: 74–75) describes as often having e-grade, root-accented bases. Olsen’s treatments of the *-tlom/*-trom family are especially important: she argues that pre-IE *-tlo- was the unmarked variant, while *-tro- arose after roots containing a liquid, while *-dʰlo-/*-dʰro- (or *-tʰlo-/*-tʰro) represented conditioned aspirated variants, especially after consonantal *h₁/*h₂, with later daughter languages often leveling one allomorph or the other (Olsen 1988: 43; Olsen 1999: 844–45). Cognates include Ancient Greek -τρον (-tron), Latin -trum , Gaulish -tron, and Sanskrit -त्र (-tra), all forming instrument or abstract nouns.