Natural development of binder (6)
I believe the answer is:
inbred
'natural' is the definition.
(similar in meaning)
'development of binder' is the wordplay.
'development of' is an anagram indicator (letters developed in another way).
'binder' is an anagram of 'INBRED'.
(Other definitions for inbred that I've seen before include "4 across" , "From too-closely-related family" , "Congenital - unwisely inter-related" , "Natural - innate" , "Was deep in thought" .)