assiduous (adj.) Look up assiduous at Dictionary.com
1530s, from Latin assiduus "attending; continually present, incessant; busy; constant," from assidere "to sit down to" (thus "be constantly occupied" at one's work); from assimilated form of ad "to" (see ad-) + sedere "to sit" (see sedentary). The word acquired a taint of "servility" in 18c. Related: Assiduously; assiduousness.