Knight with wife leaving joint in public vehicle (8)
I believe the answer is:
tristram
'public vehicle' is the definition.
The definition suggests a singular noun which matches the answer.
'knight with wife leaving joint in' is the wordplay.
'knight with' becomes 'tram' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'wife' becomes 'w'.
'leaving' indicates named letters should be taken away.
'joint' becomes 'wrist' (wrist joint is a kind of joint).
'in' means one lot of letters goes inside another.
'wrist' with 'w' removed is 'rist'.
'tram' placed around 'rist' is 'TRISTRAM'.
Can you help me to learn more?
(Other definitions for tristram that I've seen before include "Arthurian knight - Shandy" , "K" , "' - - Shandy' Sterne novel" , "Cornish knight of the Round Table" .)