Being thus addressed could give a bishop a start! (5)
I believe the answer is:
sahib
'a start' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'being thus addressed could give a bishop' is the wordplay.
I cannot really see how this works, but
'a' is present in the answer.
'bishop' could be 'b' (abbreviation for bishop in chess) and 'b' is found within the answer.
The remaining letters 'shi' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for sahib that I've seen before include "Former Indian title" , "Form of address used in India" , "Indian title of respect" , "Polite Indian title" , "Gentleman, if pukka" .)