Pedigree (4)
I believe the answer is:
line
'pedigree' is the definition.
(I know that pedigree can be written as line)
This is all the clue.
(Other definitions for line that I've seen before include "Dress" , "Railway track; policy" , "Some poetic feet; boundary, when drawn" , "A length without breadth or thickness" , "Formation of one beside another" .)