Ruled out label on double disc (5)
I believe the answer is:
taboo
'ruled out' is the definition.
(I've seen this before)
'label on double disc' is the wordplay.
'label' becomes 'tab' (I've seen this before).
'on' says to put letters next to each other.
'double' indicates the doubling of some letters.
'disc' becomes 'O' (disc-shaped letter).
'o' duplicated is 'oo'.
'tab'+'oo'='TABOO'
(Other definitions for taboo that I've seen before include "Inhibition based on social custom" , "Not to be touched or used, banned for religious reasons" , "No-no" , "Socially prohibited" , "Not allowed, forbidden, proscribed" .)