as·sid·u·ous 
(ə-sĭj-əs)
(ə-sĭj-əs)adj.
Showing or characterized by persistent attention or untiring application: an assiduous worker who strove for perfection; did assiduous research before writing the book. See Synonyms at diligent.
[From Latin assiduus, from assidēre, to attend to : ad-, ad- + sedēre, to sit; see sed- in the Appendix of Indo-European roots.]
as·sidu·ous·ly adv.
as·sidu·ous·ness n.