Merriam-Webster Collegiate Dictionary - senior

 I. noun  Etymology: Middle English, from Latin, from ~, adjective  Date: 14th century  1. a person older than another five years my ~  2.  a. a person with higher standing or rank  b. a ~ fellow of a college at an English university  c. a student in the year preceding graduation from a school of secondary or higher level  3. capitalized a member of a program of the Girl Scouts for girls in the 9th through 12th grades in school  4. ~ citizen  II. adjective  Etymology: Middle English, from Latin, older, elder, comparative of sen-, senex old; akin to Gothic sineigs old, Greek henos  Date: 14th century  1. of prior birth, establishment, or enrollment — often used to distinguish a father with the same given name as his son  2. higher ranking ; superior ~ officers  3. of, relating to, or intended for ~s a ~ center  4. having a claim on corporate assets and income prior to other securities