First to talk with successor is associated with them (5)
I believe the answer is:
their
'associated with them' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'first to talk with successor' is the wordplay.
'first to' indicates taking the first letters.
'with' is a charade indicator (letters next to each other).
'successor' becomes 'heir' (synonyms).
The first letter of 'talk' is 't'.
't'+'heir'='THEIR'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for their that I've seen before include "Belonging to those people" , "belonging to an individual" , "Some would say his (or her)" , "Relating to them" , "Belonging to him (perhaps wrongly)" .)