Leaders of busy enterprise warning worker in advance (10)
I believe the answer is:
beforehand
'in advance' is the definition.
(synonyms)
'leaders of busy enterprise warning worker' is the wordplay.
'leaders of' says to take the initial letters.
'warning' becomes 'fore' (shouted in golf).
'worker' becomes 'hand' (hand is a kind of worker).
The initial letters of 'busy enterprise' is 'be'.
'be'+'fore'+'hand'='BEFOREHAND'
(Other definitions for beforehand that I've seen before include "In advance" , "Earlier" , "Previously" .)