Hard stone urn is cut evenly (6)
I believe the answer is:
strict
'hard' is the definition.
(I've seen this before)
'stone urn is cut evenly' is the wordplay.
'stone' becomes 'st'.
'evenly' indicates alternate letters (even-numbered letters only).
'urn'+'is'+'cut'='urniscut'
The alternate letters of 'urniscut' are 'rict'.
'st'+'rict'='STRICT'
(Other definitions for strict that I've seen before include "Rigorous, uncompromising" , "Demanding that rules are observed" , "Stringent" , "Excessive pride" , "Harsh and severe" .)