Etymology tree Proto-Indo-European *wekʷ-der. Proto-Indo-European *wokʷ-der. Latin vocō Proto-Indo-European *-tḗr Proto-Indo-European *-dʰlom Proto-Indo-European *-dʰlis Proto-Italic *-ðlis Latin -bilis Latin -ābilis Old French -ablebor. Middle English -able English -able English vocable From Latin vocō + -able.