More old tartan, oddly (5)
I believe the answer is:
extra
'more' is the definition.
(I've seen this before)
'old tartan oddly' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'oddly' indicates alternate letters (letters in odd-numbered positions).
The alternating letters of 'tartan' are 'tra'.
'ex'+'tra'='EXTRA'
(Other definitions for extra that I've seen before include "Actor in non-speaking role" , "entry on scorecard?" , "bit-part player" , "Bit actor in film" , "Left over" .)