Sword, first of claymores found in former burial ground (9)
I believe the answer is:
excalibur
'sword' is the definition.
(I know that Excalibur is a sword)
'first of claymores found in former burial ground' is the wordplay.
'first of claymores' becomes 'c' (1st letter of 'claymores').
'found in' indicates putting letters inside.
'former' becomes 'ex' (prefix meaning former or onetime).
'ground' indicates an anagram ('grind' the letters into a new form).
'burial' is an anagram of 'alibur'.
'ex'+'alibur'='exalibur'
'c' put inside 'exalibur' is 'EXCALIBUR'.
(Other definitions for excalibur that I've seen before include "Steel flourished years ago" , "Legendary weapon" , "The legendary sword of King Arthur" , "King Arthur's magical sword" , "King Arthur's magic sword" .)