At the King's Head, a lion modelled in clay (6)
I believe the answer is:
kaolin
'clay' is the definition.
(I've seen this before)
'at the king's head a lion modelled' is the wordplay.
'at' means one lot of letters go next to another.
'head' indicates taking the first letters.
'modelled' indicates anagramming the letters (letters modelled or shaped).
The first letter of 'kings' is 'k'.
'lion' anagrammed gives 'olin'.
'k'+'a' is 'ka'.
'ka'+'olin'='KAOLIN'
'in' is the link.
(Other definitions for kaolin that I've seen before include "Nil oak in the ceramic clay" , "China clay" , "Soft white clay, used for making fine porcelain, say" .)