Foirm den ainmfhocal faoi thionchar focail eile in abairt. Is iad na tuisil atá sa Ghaeilge ná an tuiseal ainmneach, an tuiseal cuspóireach, an tuiseal gairmeach, an tuiseal ginideach agus an tuiseal tabharthach. (A form of the noun under the influence of another word in a sentence. The cases in Irish are the nominative case, the accusative case, the vocative case, the genitive case and the dative case.)