The Collaborative International Dictionary of English v.0.48:

Sedulous \Sed"u*lous\ (?; 135), a. [L. sedulus, perhaps from
   sedere to sit, and so akin to E. sit.]
   Diligent in application or pursuit; constant, steady, and
   persevering in business, or in endeavors to effect an object;
   steadily industrious; assiduous; as, the sedulous bee.
   [1913 Webster]

         What signifies the sound of words in prayer, without
         the affection of the heart, and a sedulous application
         of the proper means that may naturally lead us to such
         an end?                                  --L'Estrange.
   [1913 Webster]

   Syn: Assiduous; diligent; industrious; laborious;
        unremitting; untiring; unwearied; persevering.
        [1913 Webster] -- Sed"u*lous*ly, adv. --
        Sed"u*lous*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

sedulous
    adj 1: marked by care and persistent effort; "her assiduous
           attempts to learn French"; "assiduous research";
           "sedulous pursuit of legal and moral principles" [syn:
           assiduous, sedulous]

Moby Thesaurus II by Grady Ward, 1.0:

84 Moby Thesaurus words for "sedulous":
   active, ardent, assiduous, busy, constant, continuing, diligent,
   dogged, elaborate, enduring, energetic, faithful, fervent, hard,
   hardworking, hustling, immutable, inalterable, indefatigable,
   indomitable, industrious, insistent, invincible, laborious,
   lasting, loyal, never idle, never-tiring, obstinate, operose,
   painstaking, patient, patient as Job, permanent, perseverant,
   persevering, persistent, persisting, pertinacious, plodding,
   plugging, preoccupied, rapt, relentless, resolute, single-minded,
   sleepless, slogging, stable, steadfast, steady, strenuous,
   stubborn, tenacious, thorough, thoroughgoing, tireless, unabating,
   unconquerable, undaunted, undiscouraged, undrooping, unfailing,
   unfaltering, unflagging, unflinching, unintermitting,
   uninterrupted, unnodding, unrelaxing, unrelenting, unremitting,
   unsleeping, unsparing, unswerving, untiring, unwavering, unwearied,
   unwearying, unwinking, utterly attentive, vehement, weariless,
   zealous