“Prexy” or “Prex” is a slang or shortened term for a college president, originating in the 1820s. ¹⁾

Trinity College students employed the term frequently. The first uses of “Prexy” appeared on the old campus during the early or mid-19th century, and it remained popular through the mid-20th century, when it fell out of use, fashion, or institutional memory.

Merriam-Webster Dictionary

Trinity Tablet, February 1869.