Simultaneously, however (2,3,4,4)
I believe the answer is:
at the same time
This clue is a double definition.
'simultaneously' is the first definition.
(synonyms)
'however' is the second definition.
(I've seen this before)
(Other definitions for at the same time that I've seen before include "synchronised" , "nonetheless" , "together" , "Coincidentally - still - however" , "on the other hand" .)