The Collaborative International Dictionary of English v.0.48:

Stamina \Stam"i*na\ (st[a^]m"[i^]*n[.a]), n. pl.
   See Stamen.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Stamina \Stam"i*na\, n. pl.
   1. The fixed, firm part of a body, which supports it or gives
      it strength and solidity; as, the bones are the stamina of
      animal bodies; the ligneous parts of trees are the stamina
      which constitute their strength.
      [1913 Webster]

   2. Whatever constitutes the principal strength or support of
      anything; backbone; vigor; as, the stamina of a
      constitution or of life; the stamina of a State.
      [1913 Webster]

            He succeeded to great captains who had sapped the
            whole stamina and resistance of the contest. --De
                                                  Quincey.
      [1913 Webster]

   3. Hence: The power of endurance; the ability to withstand
      fatigue, disease, deprivation, etc., and continue working.
      [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Stamen \Sta"men\ (st[=a]"m[e^]n), n.; pl. E. Stamens
   (-m[e^]nz) (used only in the second sense); L. Stamina
   (st[a^]m"[i^]*n[.a]) (in the first sense). [L. stamen the
   warp, a thread, fiber, akin to Gr. sth`mwn the warp, fr.
   'ista`nai to stand, akin to E. stand. See Stand, and cf.
   Stamin, Stamina.]
   1. A thread; especially, a warp thread.
      [1913 Webster]

   2. (pl. Stamens, rarely Stamina.) (Bot.) The male organ
      of flowers for secreting and furnishing the pollen or
      fecundating dust. It consists of the anther and filament.
      [1913 Webster]

WordNet (r) 3.0 (2006):

stamina
    n 1: enduring strength and energy [syn: stamina, staying
         power, toughness]

Moby Thesaurus II by Grady Ward, 1.0:

116 Moby Thesaurus words for "stamina":
   application, assiduity, assiduousness, backbone, balls, bottom,
   bulldog tenacity, chutzpah, cohesiveness, concentration, constancy,
   courage, decisiveness, diligence, dogged perseverance, doggedness,
   durability, endurance, energy, engrossment, fidelity, force,
   fortitude, gameness, grit, guts, gutsiness, guttiness, hardiness,
   hardness, heart, heart of oak, heartiness, indefatigability,
   indomitability, industriousness, industry, infrangibility,
   insistence, insistency, intestinal fortitude, lastingness,
   leatherlikeness, loyalty, lustihood, lustiness, mettle,
   mettlesomeness, might, mightiness, moxie, nerve, obstinacy,
   patience, patience of Job, permanence, perseverance, persistence,
   persistency, pertinaciousness, pertinacity, pith, plodding, pluck,
   pluckiness, plugging, potency, power, powerfulness, preoccupation,
   relentlessness, resistance, resolution, robustness, ropiness,
   ruggedness, sand, sedulity, sedulousness, single-mindedness,
   singleness of purpose, slogging, spirit, spunk, spunkiness,
   stability, stalwartness, starch, staunchness, staying power,
   steadfastness, steadiness, stick-to-itiveness, sticking power,
   stiffness, stout heart, stoutness, strength, strength of will,
   stringiness, stubbornness, sturdiness, tenaciousness, tenacity,
   tirelessness, toleration, toughness, true grit, unbreakability,
   unbreakableness, unremittingness, unswerving attention, vigor,
   vigorousness, viscidity, vitality