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' says to put letters next to each other.
'head' suggests taking the first letters.
'modelled' is an anagram indicator (I've seen 'model' mean this).
The initial letter of 'kings' is 'k'.
'lion' is an anagram of 'olin'.
'k'+'a' is 'ka'.
'ka'+'olin'='KAOLIN'
'in' acts as a 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" .)