"Uh, excuse me . . ." (4)
I believe the answer is:
ahem
'uh excuse me' 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 "Utterance of mild disapproval" , "Expression of disapproval" , "attention-seeker?" , "Sound used to attract attention" , "Attention-getter" .)