Lead on East, with diamonds to support no-trumps (6)
I believe the answer is:
entice
'lead on' is the definition.
(thesaurus)
'east with diamonds to support no-trumps' is the wordplay.
'east' becomes 'e' ('E' can be a synonym of 'east').
'with' is a charade indicator (letters next to each other).
'diamonds' becomes 'ice' (I've seen this before).
'to support' is a charade indicator (letters next to each other) (in a down clue, some letters hold others up).
'no trumps' becomes 'nt'.
'ice' after 'nt' is 'ntice'.
'e'+'ntice' is 'ENTICE'.
(Other definitions for entice that I've seen before include "Lure, inveigle" , "Trap" , "Coax" , "Attract with offers" , "'Tempt, lure (6)'" .)