Watchful old retainer escorting bishop (9)
I believe the answer is:
observant
'watchful' is the definition.
(I've seen this before)
'old retainer escorting bishop' is the wordplay.
I cannot quite see how this works, but
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is located in the answer.
'retainer' could be 'servant' (synonyms) and 'servant' is found in the answer.
'bishop' could be 'b' (abbreviation used in chess) and 'b' is present in the answer.
No letters remain.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for observant that I've seen before include "Alert" , "Likely to notice" , "keeping close eye on things" , "taking things in" , "Sharp-eyed" .)