In Irish Gaelic, "dílis" is usually an adjective meaning "faithful, dear, proper...". The two main Irish/English dictionaries (Dineen and O'Donnell) give "díleas" as both an alternative spelling for that adjective and as a noun, as outlined by Jim above. Can't say I've ever noticed that spelling and usage in practice - it may well be regional.

For Irish, michaelr's phonetic pronunciation "dee-lish" is fine with the stress on the first syllable.

Regards