Element of tradition in this anniversary marked with pottery (5)
I believe the answer is:
ninth
'anniversary marked with pottery' is the definition.
(pottery is gifted for ninth wedding anniversaries)
'element of tradition in this' is the wordplay.
'element of' says the answer is hidden in the clue (I've seen this in other clues).
'NINTH' is hidden in the letters of 'tradition in this'.
(Other definitions for ninth that I've seen before include "Eg, Beethoven's choral symphony" , "interval" , "One over the eighth" , "Beethoven's "Choral", for example" , "Ordinal number" .)