"Say what?" (4,5)
'say what?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for huh that I've seen before include "Palindromic exclamation of disgust or surprise" , "sorry?" , "Expression of disgust or surprise" .)
(Other definitions for come again that I've seen before include "Please clarify" , "You were great company" , "You're welcome to return - pardon?" , "Turn out once more" , "What did you say? - egomaniac (anag)" .)