Tell on nobleman (7)
I believe the answer is:
recount
'tell' is the definition.
(synonyms)
'on nobleman' is the wordplay.
'on' becomes 're' (regarding).
'nobleman' becomes 'count' (count is a type of aristocrat).
're'+'count'='RECOUNT'
(Other definitions for recount that I've seen before include "Go over details" , "Communicate" , "Check numbers" , "post-election procedure?" , "Give report" .)