Money — holding krona ultimately in both hands is key (7)
I believe the answer is:
central
'is key' is the definition.
(synonyms)
'money holding krona ultimately in both hands' is the wordplay.
'money' becomes 'cent' (I've seen this before).
'holding' is a charade indicator (letters next to each other).
'ultimately' indicates one should take the final letters.
'in' is an insertion indicator.
'both hands' becomes 'rl'.
The final letter of 'krona' is 'a'.
'a' placed within 'rl' is 'ral'.
'cent'+'ral'='CENTRAL'
(Other definitions for central that I've seen before include "Every answer here has one such letter" , "Most important, principal" , "Near the middle" , "Focal" , "Key" .)