Green Party finally contrived to get power (6)
I believe the answer is:
energy
'power' is the definition.
('energy' can be a synonym of 'power')
'green party finally contrived' is the wordplay.
'finally' indicates one should take the final letters.
'contrived' is an anagram indicator.
The final letter of 'party' is 'y'.
'green'+'y'='greeny'
'greeny' anagrammed gives 'ENERGY'.
'to get' acts as a link.
(Other definitions for energy that I've seen before include "Power - drive" , "Vitality, get-up-and-go" , "Vivacity" , "life" , "Capacity for action" .)