sedulous

No fooling-the word sedulous ultimately comes from the Latin se dolus, which literally means "without guile." Those two words were eventually melded into one, sedulo, meaning "sincerely" or "diligently," and from that root developed Latin sedulus and English "sedulous." Don’t let the "sed-" beginning mislead you; "sedulous" is not related to words such as "sedentary" or "sedate" (which derive from the Latin verb sedēre, meaning "to sit"). "Sedulous" people are not the sedate or sedentary sort. They're the hardworking types Scottish author Samuel Smiles must have had in mind when he wrote in his 1859 book Self-Help, "Sedulous attention and painstaking industry always mark the true worker."