Officer, Celt - one I mistook in time for voting (7,8)
I believe the answer is:
general election
'time for voting' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'officer celt one i mistook' is the wordplay.
'officer' becomes 'general' (general is a kind of officer).
'mistook' indicates an anagram.
'celt'+'one'+'i'='celtonei'
'celtonei' anagrammed gives 'election'.
'general'+'election'='GENERAL ELECTION'
'in' is the link.
Can you help me to learn more?
(Other definitions for general election that I've seen before include "representative selection" , "Poll" , "When all MPs are chosen" .)