Spelling bee word again.'
sedulous - 1540, from L. sedulus "attentive, painstaking,"
probably from sedulo (adv.) "sincerely, diligently," from
sedolo "without deception or guile," from se- "without" +
dolo, ablative of dolus "deception, guile."

And I have to admit for years entertaining "folk etymology" that it meant "sitting studiously"