"gh" and "dh" are both pronounced as a somewhat guttural "ch" i.e. a bit further back in the mouth - a difficult sound for non-Gaels. A non-initial "d" iis always pronounced "t". The "a" is also longer than it would be in English.
The word is probably related to early French "cadis" = serge. French, of course, may have got it from early Celtic.

Alan