Studious comes from Latin studiōsus ('eager, diligent, devoted to study'), from studium ('zeal, application, study'), from studēre ('to be eager, apply oneself'). The historical chain includes Latin studiōsus and Latin studēre. The quoted older senses, "eager, diligent, devoted to study", "zeal, application, study", and "to be eager, apply oneself", supply the semantic anchors for studious. The formation is best read as borrowed: the word studious carries its older form-history into a compact English lexical shape. In present English it is used as a adj, "devoted to study; diligent and careful". English derivatives include studiously and studiousness; related English forms include study, student, and studio. The result is a adj whose etymology preserves both the older form and the later English specialization.