"Beg pardon" (4)
(Other definitions for what that I've seen before include "I beg your pardon" , "Interrogatory word" , "Eh?" , "Word used in a question" , "I didn't hear" .)
'beg pardon' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ahem that I've seen before include "Polite noise to draw attention" , "Throat clearing sound to catch attention" , "It attracts attention" , "Attention-getter" , "that's said to attract attention" .)