/
ˈsiːnɪə, 
ˈsiːnjə/
adj.
   - for or denoting older people. 
▸Brit. for or denoting schoolchildren above a certain age, typically eleven.
 ▸US of the final year at a university or high school.
 - 
[postpos.]
 denoting the elder of two with the same name in a family.
 - high or higher in rank or status.
 
n.
    - a person who is a specified number of years older than someone else:
 she was two years his senior.
 - a student in one of the higher forms of a senior school.
 - (in sport) a competitor of above a certain age or of the highest status.
 - an elderly person, especially an old-age pensioner.
 
Derivative
Etymology
ME: from L., lit. ‘older, older man’, compar. of senex, sen- ‘old man, old’.