Discover incomplete part of the family tree (7)
I believe the answer is:
uncloak
'discover' is the definition.
(thesaurus)
'incomplete part of the family tree' is the wordplay.
'incomplete' means to remove the last letter.
'part of the family' becomes 'uncle' (type of relative).
'tree' becomes 'oak' (oak is a type of tree).
'uncle' with its final letter taken away is 'uncl'.
'uncl'+'oak'='UNCLOAK'
(Other definitions for uncloak that I've seen before include "Bare" , "[SHOW] (1 of 2)" .)