An attic up high
I believe the answer is:
aloft
'up high' is the definition.
(I've seen this before)
'an attic' is the wordplay.
'an' becomes 'a'.
'attic' becomes 'loft' (synonyms).
'a'+'loft'='ALOFT'
(Other definitions for aloft that I've seen before include "up the mast" , "Up in the air, high above" , "At a considerable height" , "Up in the sky" , "at high altitude" .)