"Good heavens!" (4)
(Other definitions for egad that I've seen before include "traditional oath" , "Mild oath - aged (anag)" , "Archaic exclamation of surprise" , "Forgotten curse" , "Christ" .)
'good heavens' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for my word that I've seen before include "gracious" , "Gosh!" , "Well I'm blowed!" , "This seals promise I make" , "What I would give to guarantee" .)
(Other definitions for i say that I've seen before include "Blimey!" , "Dear me!" , "Look here; oh, my" , "goodness!" , "Gosh!" .)