Watch former pupil and wait (7)
I believe the answer is:
observe
'watch' is the definition.
(synonyms)
'former pupil and wait' is the wordplay.
'former pupil' becomes 'OB' (abbreviation for 'Old Boy' - private school pupil).
'and' means one lot of letters go next to another.
'wait' becomes 'serve' (to wait on someone is to serve them).
'ob'+'serve'='OBSERVE'
(Other definitions for observe that I've seen before include "Watch, take note of" , "See - keep - remark - maintain - celebrate" , "Notice; study" , "Keep an eye on" , "Witness, watch" .)