1 American EnglishSESSEC
a student in their last year of high school or university [↪ freshman, junior, sophomore]:
Jen will be a senior this year.
2 especially American English
a senior citizen:
Seniors can get a 10% discount.
to be two, five, ten etc years older than someone:
Her husband was nine years her senior.
4 British English
an adult or a person who has reached an advanced level in a particular sport [↪ junior]:
Juniors and seniors train together on Wednesdays.