Meaning

noun an undergraduate student during the year preceding graduation

noun a person who is older than you are

adjective older; higher in rank; longer in length of tenure or service

originFrom Middle English senior, from Latin senior (“older”), comparative form of senex (“old”); see senate. Doublet of seigneur, seignior, senhor, señor, senyor, signore, sir, and sire.

Etymology from Wiktionary, CC BY-SA 3.0