Oak. Written Dara, Darragh, Dare — the same Irish word, dara / dair, in the spellings English gave it.
Oak: it is the Irish dara / dair. It is written Dara, Darragh, Dare in English spellings of Irish names.
dara / dair. English spellings of the same word include Dara, Darragh, Dare, because the names were written down by ear.
Kildare (Cill Dara), Adare (Áth Dara).