Spook just seen in bog (8)
I believe the answer is:
frighten
'spook' is the definition.
(thesaurus)
'just seen in bog' is the wordplay.
'just' becomes 'right' ('right' can be similar in meaning to 'just').
'seen in' indicates putting letters inside.
'bog' becomes 'fen'.
'right' inserted into 'fen' is 'FRIGHTEN'.
(Other definitions for frighten that I've seen before include "Cow" , "Scare, alarm" , "Terrify" , "Cause alarm" , "Spook" .)