"That's not good . . ." (2-2)
'that's not good' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for yikes that I've seen before include "by George" , "Watch out" , "Exclamation of surprise or alarm" , "Gosh! - Oh no!" , "Expression of alarm or astonishment" .)