Source of inspiration and great power in the writer (4)
I believe the answer is:
muse
'source of inspiration' is the definition.
(I've seen this before)
'great power in the writer' is the wordplay.
'great power' becomes 'US' (United States, global superpower).
'in the' is an insertion indicator.
'writer' becomes 'me' (the person who wrote the clues).
'us' placed inside 'me' is 'MUSE'.
'and' is the link.
(Other definitions for muse that I've seen before include "Ponder in meditative way" , "Meditate on a goddess of the arts" , "Goddess; rock group" , "Inspiring goddess" , "The source of an artist's inspiration" .)