Fancy crest adopted by one unspecified family (8)
I believe the answer is:
ancestry
'family' is the definition.
(I've seen this before)
'fancy crest adopted by one unspecified' is the wordplay.
'fancy' indicates an anagram.
'adopted by' means one lot of letters goes inside another (I've seen this in other clues).
'one unspecified' becomes 'any' (any example of something).
'crest' anagrammed gives 'cestr'.
'cestr' placed within 'any' is 'ANCESTRY'.
(Other definitions for ancestry that I've seen before include "Blood line" , "race" , "Genealogy" , "Family tree" , "Line of forebears" .)