Worker one finds hostile (4)
I believe the answer is:
anti
'hostile' is the definition.
(thesaurus)
'worker one' is the wordplay.
'worker' becomes 'ant' (worker is a type of ant**).
'one' becomes 'i' (Roman numeral).
'ant'+'i'='ANTI'
'finds' acts as a link.
(Other definitions for anti that I've seen before include "Who pooh-poohs all" , "One who is against (something)" , "Opposed to followers of Hitler" , "on the other side" , "[NO MAN]" .)