Singular P&O leaders in new squabble over retirement fund (7)
I believe the answer is:
sponsor
'fund' is the definition.
(thesaurus)
'singular po leaders in new squabble over retirement' is the wordplay.
'singular' becomes 's' (abbreviation sometimes used in dictionaries).
'leaders in' indicates taking the first letters.
The initial letters of 'new squabble over retirement' is 'nsor'.
's'+'po'+'nsor'='SPONSOR'
(Other definitions for sponsor that I've seen before include "Provide finance for" , "One paying for, eg, event" , "Promoter, godparent" , "One financially supporting an activity" , "One who pays costs for event" .)