Party leader's latest welcome (4)
I believe the answer is:
rave
'party' is the definition.
(thesaurus)
'leader's latest welcome' is the wordplay.
'latest' says to take the final letters.
'welcome' becomes 'ave' (I've seen this before).
The final letter of 'leader' is 'r'.
'r'+'ave'='RAVE'
(Other definitions for rave that I've seen before include "Modern youth dance - sounds hysterical" , "Rant about an all-night dance party?" , "Pop dance party" , "Rapturous" , "Party with electronic dance music - be wild" .)