From Old Irish turchur.
turchair (past thurchair, future turchairidh, verbal noun turchairt)
- happen, chance
Thurchair dhaibh a thighinn dhachaigh aig an aon àm. ― They happened to come home at the same time.
a thurchair a bhith a' dol seachad ― who happened/chanced to be passing by.
nan turchradh dhuinn a bhith ― if we happen to be
Thurchair mi air. ― I chanced on it / I met him by chance.
- “turchur” in Dictionary of the Irish Language, Royal Irish Academy, 1913–76.