Accelerate to gain ground (7)
I believe the answer is:
advance
I believe this is a double definition.
'accelerate' is the first definition.
(thesaurus)
'gain ground' is the second definition.
('advance' can be a synonym of 'gain ground')
'to' is the link.
(Other definitions for advance that I've seen before include "Make headway" , "Move forward to get loan?" , "Put forward (a theory)" , "Forward - loan - make progress" , "Early" .)