Affair with brute rendered one uncertain (7)
I believe the answer is:
doubter
'one uncertain' is the definition.
I can't judge whether this definition defines the answer.
'affair with brute rendered' is the wordplay.
'affair' becomes 'do' (do is a kind of affair).
'with' says to put letters next to each other.
'rendered' is an anagram indicator (letters rendered in a new form).
'brute' is an anagram of 'ubter'.
'do'+'ubter'='DOUBTER'
Can you help me to learn more?
(Other definitions for doubter that I've seen before include "E.g. St Thomas" , "one such as Thomas" , "One who is not sure" .)