Black knight pens song for Scots child (5)
I believe the answer is:
bairn
'scots child' is the definition.
(I've seen this before)
'black knight pens song' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'knight' becomes 'n' (chess).
'pens' indicates putting letters inside.
'song' becomes 'air' (I've seen this before).
'b'+'n'='bn'
'bn' going around 'air' is 'BAIRN'.
'for' is the link.
(Other definitions for bairn that I've seen before include "Northern child" , "Wee child" , "Scot. child" , "A tot of Scotch" , "A Scottish child?" .)