Cáilíocht ainmfhocail a fhágann de ghnáth gur féidir é a rá leis nuair atá sé firinscneach agus í nuair atá sé baininscneach. Tá gach ainmfhocal sa Ghaeilge firinscneach nó baininscneach. Go hiondúil, freagraíonn focal firinscneach do rud atá fireann, agus focal baininscneach do rud atá baineann, ach tá eisceachtaí áirithe ann. Tá an focal cailín baininscneach, mar shampla. (A noun qualification which normally means that é can be used with it when it is masculine or í when it is feminine. Normally, a masculine word denotes a thing that is masculine, and a feminine word denotes a thing that is feminine, but there are certain exceptions. The word cailín is masculine, for example.)