"diligence," early 15c., from Latin assiduitatem (nominative assiduitas) "continual presence," noun of quality from assiduus "continually present" (see assiduous).
Industry keeps at work, leaving no time idle. Assiduity (literally, a sitting down to work) sticks quietly to a particular task, with the determination to succeed in spite of its difficulty, or to get it done in spite of its length. Application, literally, bends itself to its work, and is, more specifically than assiduity, a steady concentration of one's powers of body and mind .... [Century Dictionary]
Others are reading