Dispute source of apparently irrational urge (5)
I believe the answer is:
argue
'dispute' is the definition.
(thesaurus)
'source of apparently irrational urge' is the wordplay.
'source of' indicates taking the first letters.
'irrational' is an anagram indicator.
The initial letter of 'apparently' is 'a'.
'urge' is an anagram of 'rgue'.
'a'+'rgue'='ARGUE'
(Other definitions for argue that I've seen before include "Exchange heated views" , "Debate, contest verbally" , "contradict" , "express disagreement" , "Disagree violently" .)