Begin doubting urge to discard (5)
I believe the answer is:
ditch
'discard' is the definition.
(thesaurus)
'begin doubting urge' is the wordplay.
'begin' indicates taking the first letters.
'urge' becomes 'itch' (I've seen this before).
The first letter of 'doubting' is 'd'.
'd'+'itch'='DITCH'
'to' acts as a link.
(Other definitions for ditch that I've seen before include "Boundary trench" , "Get rid of; dug channel" , "Throw away (sl.)" , "Drop" , "Drainage channel" .)