Heir to drop worker (10)
I believe the answer is:
descendant
'heir' is the definition.
(thesaurus)
'drop worker' is the wordplay.
'drop' becomes 'descend' (I've seen this in another clue).
'worker' becomes 'ant' (worker is a type of ant).
'descend'+'ant'='DESCENDANT'
'to' is the link.
(Other definitions for descendant that I've seen before include "One from a long line" , "Grandson maybe" , "Later family member" , "Future person in one's family line" , "Progeny" .)