The Collaborative International Dictionary of English v.0.48:

Industrious \In*dus"tri*ous\, a. [L. industrius, industriosus:
   cf. F. industrieux. See Industry.]
   [1913 Webster]
   1. Given to industry; characterized by diligence; constantly,
      regularly, or habitually occupied; busy; assiduous; not
      slothful or idle; -- commonly implying devotion to lawful
      and useful labor.
      [1913 Webster]

            Frugal and industrious men are commonly friendly to
            the established government.           --Sir W.
                                                  Temple.
      [1913 Webster]

   2. Steadily and perseveringly active in a particular pursuit
      or aim; as, he was negligent in business, but industrious
      in pleasure; an industrious mischief maker.
      [1913 Webster]

            Industrious to seek out the truth of all things.
                                                  --Spenser.
      -- In*dus"tri*ous*ly, adv. -- In*dus"tri*ous*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

industrious
    adj 1: characterized by hard work and perseverance [syn:
           hardworking, industrious, tireless, untiring]
    2: working hard to promote an enterprise [syn: energetic,
       gumptious, industrious, up-and-coming]

Moby Thesaurus II by Grady Ward, 1.0:

91 Moby Thesaurus words for "industrious":
   active, aggressive, ardent, assiduous, busy, conscientious,
   constant, continuing, diligent, dogged, dynamic, elaborate,
   enduring, energetic, faithful, fervent, hard, hard-working,
   hardworking, hustling, immutable, inalterable, indefatigable,
   indomitable, insistent, intense, invincible, laborious, lasting,
   live, loyal, never idle, never-tiring, obstinate, operose,
   painstaking, patient, patient as Job, permanent, perseverant,
   persevering, persistent, persisting, pertinacious, plodding,
   plugging, preoccupied, rapt, relentless, resolute, sedulous,
   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, vigorous,
   weariless, zealous