Dysert (dye-sert) is Irish for a hermitage for monks.It is related to the English word "desert".
O'Dea in Irish is pronounced closer to "O'Day".Modern folk in Ireland tend to pronounce the name "O'Dee", as in Jimmy O'Dea, the actor.Some in Clare, where the name originated, still pronounce it "O'Day".
Perhaps our Gaelic speaking forbearers came to the new world retianing the Gaelic pronunication which has since been lost by our cousins in the 'auld sode'.
It is interesting to note that the name is usually pronounced, and often spelled,"O'Day" where it occurs in Canada, Australia and USA even though the uninitiated would tend to pronounce 'O'Dea' as 'O'Dee' based on rules of English pronunciation.
Odea is the plural of odeum, an ancient Greek theatre.Remember that for crossword puzzles!