Irish taoiseach

← Proto-Celtic *towissākos (inherited)

← Welsh tywysog (cognate)

← Proto-Indo-European *wedʰ- (inherited)

← Proto-Indo-European *weyd- (mention)

← Primitive Irish ᚈᚑᚃᚔᚄᚐᚉᚔ (inherited)

← Old Irish toísech (inherited)

→ English taoiseach (mention)

→ Irish tosach (mention)