"Excuse me ..." (4)
'excuse me' is the definition.
(both might be said to get someone's attention)
This is all the clue.
(Other definitions for ahem that I've seen before include "Half-cough to draw attention" , "Polite noise to draw attention" , "Throat-clearing noise?" , "attention-seeker?" , "It attracts attention" .)
(Other definitions for what that I've seen before include "Eh?" , "I beg your pardon" , "Word used in a question" , "Interrogatory word" , "That which - come again!" .)
(Other definitions for oops that I've seen before include "Silly me, I've dropped something!" , "Oh dear, that's a mistake!" , "Exclamation on making obvious mistake" , "I've messed up" , "Something's been spilt!" .)
(Other definitions for pardon that I've seen before include "indulgence" , "Forgive the polite interruption" , "Forgiveness - I beg yours" , ""I'm sorry, could you say that again?"" , "Forgiveness for an offence" .)