Relation to resist plan (6)
I believe the answer is:
sister
'relation' is the definition.
(I know that sister subproperty of relation)
'resist plan' is the wordplay.
'plan' indicates an anagram (plan can mean organise).
'resist' with letters rearranged gives 'SISTER'.
'to' is the link.
(Other definitions for sister that I've seen before include "Nun's title" , "twin?" , "Tender" , "Resist about the sibling" , "A kinswoman" .)