Reject fool for opening seedy club (10)
I believe the answer is:
disapprove
'reject' is the definition.
(I know that reject can be written as disapprove)
'fool for opening seedy club' is the wordplay.
'fool' becomes 'sap' (synonyms).
'for' becomes 'pro' (as in being 'pro' something).
'opening' indicates putting letters inside (some letters open a gap in others).
'seedy club' becomes 'dive'.
'sap'+'pro'='sappro'
'sappro' placed into 'dive' is 'DISAPPROVE'.
(Other definitions for disapprove that I've seen before include "Not like" , "Reject" , "Censure" , "Hold an unfavourable opinion (of something)" , "mind" .)