Hide in attic once alone (7)
I believe the answer is:
'hide' is the definition.
(I know that hide can be written as conceal)
'in attic once alone' is the wordplay.
'in' says the answer is hidden in the clue.
'CONCEAL' is hidden in the letters of 'attic once alone'.
(Other definitions for conceal that I've seen before include "hush up!" , "Screen" , "Hide, cover" , "Keep out of sight" , "Place out of sight" .)