Elder (6)
'elder' is the definition.
(similar in meaning)
This is the entire clue.
(Other definitions for senior that I've seen before include "Higher in status" , "Pupil in a higher form" , "Denoting older people" , "Higher in rank or age" , "Older in years or higher in rank" .)
'elder' is the definition.
(synonyms)
This is all the clue.
(Other definitions for older that I've seen before include "More ancient" , "More aged" , "More senior" , "More advanced in point of time" , "Less young" .)