Could be alien to high spirits (7)
I believe the answer is:
elation
'high spirits' is the definition.
(synonyms)
'could be alien to' is the wordplay.
'could be' indicates an anagram.
'alien'+'to'='aliento'
'aliento' with letters rearranged gives 'ELATION'.
(Other definitions for elation that I've seen before include "exhibits successful pride" , "Ecstasy -- toenail (anag)" , "Exaltation" , "Transport" , "Delight, ecstasy" .)