Is it ensure, insure, or assure?
1620s, "university degree of a bachelor," from Medieval Latin baccalaureatus, from baccalaureus "student with the first degree," altered by a play on words with bacca lauri "laurel berry" (laurels being awarded for academic success).
The Medieval Latin word perhaps ultimately is derived from Latin baculum "staff" (see bacillus), which the young student might carry, but it is more likely just a re-Latinization of bachelor (q.v.) in its academic sense. In modern U.S. usage, the word usually is short for baccalaureate-sermon (1864), a religious farewell address to the graduating class.