Tell of a second reckoning (7)
I believe the answer is:
recount
'tell' is the definition.
(I know that tell can be written as recount)
'a second reckoning' is the wordplay.
'a second' becomes 're' (prefix meaning second in eg review, re-education).
'reckoning' becomes 'count' (synonyms).
're'+'count'='RECOUNT'
'of' acts as a link.
(Other definitions for recount that I've seen before include "Tell - check on election result" , "possible action when votes are checked" , "reason for lateness of election result?" , "electoral process" , "Tell in detail" .)