cú or chú
aon causes lenition of the following word, so cù is ‘a dog’, but ‘one dog’ is aon chù.
Aon does not cause lenition of words starting with dental consonants (d, t, s), so aon deoch ‘one drink’ (and not *aon dheoch).
Joe, your diacritics are Irish-style! Scottish 'accents' go top-left to bottom-right.