Notice old bishop beginning to rally (7)
I believe the answer is:
observe
'notice' is the definition.
(I know that notice is a more specific form of observe)
'old bishop beginning to rally' is the wordplay.
'beginning to' suggests taking the first letters.
'rally' becomes 'serve' (I can't explain this - if you can you should believe this answer much more).
The first letters of 'old bishop' is 'ob'.
'ob'+'serve'='OBSERVE'
Can you help me to learn more?
(Other definitions for observe that I've seen before include "Notice or conform to, rules say" , "Notice, watch" , "Discern" , "Notice, perceive" , "Notice; study" .)