PIE base ‘instrument, tool’, suffix creating nouns from verbs.
Other derivatives include Old English -þor, in rōþor ‘instrument used for rowing, rudder’; Greek -tron, in arotron ‘a plough’; Latin -trum, in rastrum ‘rake, an instrument for scraping’; and plectrum ‘tool for plucking strings’, from Greek via Latin.
Not in Pokorny.