High up — in an attic? (5)
I believe the answer is:
aloft
'high up' is the definition.
(synonyms)
'an attic?' is the wordplay.
'an' becomes 'a'.
'attic?' becomes 'loft' (synonyms).
'a'+'loft'='ALOFT'
'in' is the link.
(Other definitions for aloft that I've seen before include "Above - on top" , "Animistic cult" , "Heading for heaven" , "Skyward" , "at high altitude" .)