Dump date before long (5)
I believe the answer is:
ditch
'dump' is the definition.
(thesaurus)
'date before long' is the wordplay.
'date' becomes 'd' (common abbreviation eg in DOB, date of birth).
'before' means one lot of letters go next to another.
'long' becomes 'itch' (I've seen this before).
'd'+'itch'='DITCH'
(Other definitions for ditch that I've seen before include "Drainage trench" , "Excavated channel" , "Throw away - trench" , "Dyke" , "Dug water channel" .)