Source : Webster's Revised Unabridged Dictionary (1913)

Tenacious \Te*na"cious\, a. [L. tenax, -acis, from tenere to
   hold. See {Tenable}, and cf. {Tenace}.]
   1. Holding fast, or inclined to hold fast; inclined to retain
      what is in possession; as, men tenacious of their just
      rights.

   2. Apt to retain; retentive; as, a tenacious memory.

   3. Having parts apt to adhere to each other; cohesive; tough;
      as, steel is a tenacious metal; tar is more tenacious than
      oil. --Sir I. Newton.

   4. Apt to adhere to another substance; glutinous; viscous;
      sticking; adhesive. ``Female feet, too weak to struggle
      with tenacious clay.'' --Cowper.

   5. Niggardly; closefisted; miserly. --Ainsworth.

   6. Holding stoutly to one's opinion or purpose; obstinate;
      stubborn. -- {Te*na"cious*ly}, adv. -- {Te*na"cious*ness},
      n.

Source : WordNet®

tenaciousness
     n : persistent determination [syn: {doggedness}, {perseverance},
          {persistence}, {persistency}, {tenacity}, {pertinacity}]