Developing state aim and theme simultaneously (2,3,4,4)
I believe the answer is:
at the same time
'simultaneously' is the definition.
('at the same time' can be a synonym of 'simultaneously')
'developing state aim and theme' is the wordplay.
'developing' indicates an anagram.
'and' means one lot of letters go next to another (I've seen this in other clues).
'state'+'aim'='stateaim'
'stateaim' after 'theme' is 'themestateaim'.
'themestateaim' with letters rearranged gives 'AT THE SAME TIME'.
(Other definitions for at the same time that I've seen before include "Simultaneously - nevertheless" , "Notwithstanding" , "Coincidentally - still - however" , "on the other hand" , "synchronised" .)