In retrospect, reached for spirit (7)
I believe the answer is:
spectre
'spirit' is the definition.
(I know that spectre is a type of spirit)
'in retrospect reached for' is the wordplay.
'in' indicates a hidden word.
'SPECTRE' can be found hidden inside 'retrospect reached for'.
(Other definitions for spectre that I've seen before include "Respect for a ghost" , "Ghostly figure" , "Enemy organisation for James Bond; ghost" , "Sceptre (anag.)" , "'Phantom, shade (7)'" .)