US state keeps Republican jolly (6)
I believe the answer is:
marine
'jolly' is the definition.
(thesaurus)
'us state keeps republican' is the wordplay.
'us state' becomes 'maine' (I've seen this before).
'keeps' indicates putting letters inside.
'republican' becomes 'r' (abbreviation).
'maine' going around 'r' is 'MARINE'.
(Other definitions for marine that I've seen before include "Maritime - seagoing soldier" , "jolly" , "seaman" , "Sea-soldier" , "Concerning the sea" .)