Deceitful and silly U-turn over Ecstasy (6)
I believe the answer is:
untrue
'deceitful' is the definition.
(thesaurus)
'silly u-turn over ecstasy' is the wordplay.
'silly' is an anagram indicator.
'over' means one lot of letters go next to another (in a down clue, some letters go over others).
'ecstasy' becomes 'E' (informal term for the drug).
'u'+'turn'='uturn'
'uturn' is an anagram of 'untru'.
'untru'+'e'='UNTRUE'
'and' is the link.
(Other definitions for untrue that I've seen before include "Spurious" , "Not factual or honest" , "Not loyal" , "Not in accordance with the facts" , "Sleeping around" .)