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