Sap departs dressed in a continental fur (9)
I believe the answer is:
undermine
'sap' is the definition.
(thesaurus)
'departs dressed in a continental fur' is the wordplay.
'departs' becomes 'd' (common abbreviation e.g. train timetables).
'dressed in' is an insertion indicator.
'a continental' becomes 'un' (the word 'a' as said on the European continent).
'fur' becomes 'ermine' (ermine is a kind of fur**).
'un'+'ermine'='unermine'
'd' placed into 'unermine' is 'UNDERMINE'.
(Other definitions for undermine that I've seen before include "Weaken insidiously" , "Erode the base or foundation of" , "Erode foundations" , "Subvert or weaken gradually" , "Burrow below" .)