Observed some Old Etonians making a comeback (5)
I believe the answer is:
noted
'observed' is the definition.
('note' can be a synonym of 'observe')
'some old etonians making a comeback' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'making a comeback' says the letters should be written in reverse.
'deton' is hidden within 'old etonians'.
'deton' reversed gives 'NOTED'.
(Other definitions for noted that I've seen before include "Famed" , "Remarkable" , "Observed - recorded" , "Toned down and recorded" , "Renowned" .)