Cheers and jeers are forbidden (6)
I believe the answer is:
taboos
'are forbidden' is the definition.
(a taboo forbids or discourages something)
'cheers and jeers' is the wordplay.
'cheers' becomes 'ta' (both can mean thank you).
'and' says to put letters next to each other.
'jeers' becomes 'boos' (boos from a crowd).
'ta'+'boos'='TABOOS'
(Other definitions for taboos that I've seen before include "restrictions" , "Superstitious bans or prohibitions" , "Prejudices that prohibit the mention of something" , "Prohibitions on things not to be done" , "Prohibitions buy custom or religion" .)