Sentence:  Bede's work, which remained in active use for half a millennium, stood at the very center of the university curriculum, because the mastery of <WSD>computus</WSD> included many different essential subjects such as astronomy, mathematics, geography, theology, and law; its applications, too, included medicine and agriculture. 
Meaning of the word marked with <WSD> tags:  The calculation of the date of Easter in the Christian calendar.