I'm posting a little later than usual, but lucky the US is in the distant past, so it's all good!
A medical certificate of illness excusing student's sickness. Rarely used today except in Britain, and then only in the context of degrees and courses considered as passed by a student too ill to finish the appropriate material. Aegrotat is the only surviving remnant of the Latin verb aegrotare.
From Latin aegrotat, 'he or she is sick,' 3rd person singular of aegrotare, from aeger, 'sick.'
Having spent much of the year recovering from a nasty accident, Bill got excused from his studies and was allowed to complete it later with the provision of an aegrotat. His dorm-mate, Jim, wondered if he could get one too - well, being hungover was a kind of illness, and he was frequently ill!