why do abairt and ollscoil, both of which are feminine, not take "t-" with the definite article? That is, why "an abairt" and not "an t-abairt"? I'm sure the answer is obvious but I can't find it. Thanks.
Only nominative singular masculine nouns that begin with a vowel get a t- prefix following an. It’s nominative singular feminine nouns (and genitive singular masculine nouns) that begin with S followed by L, N, R, or a vowel that get a t prefix (unhyphenated) following an.