Prior; ancestor (10)
I believe the answer is:
This clue is a double definition.
'prior' is the first definition.
(similar in meaning)
'ancestor' is the second definition.
(I know that ancestor can be written as antecedent)
(Other definitions for antecedent that I've seen before include "Going before (in time/order)" , "Preceding in time or order" , "Something logically preceding another" , "Something existing before another" , "Previous" .)