The Collaborative International Dictionary of English v.0.48:

Stoicism \Sto"i*cism\, n. [Cf. F. sto["i]cisme.]
   1. The opinions and maxims of the Stoics.
      [1913 Webster]

   2. A real or pretended indifference to pleasure or pain;
      insensibility; impassiveness.
      [1913 Webster]

WordNet (r) 3.0 (2006):

stoicism
    n 1: an indifference to pleasure or pain [syn: stoicism,
         stolidity, stolidness]
    2: (philosophy) the philosophical system of the Stoics following
       the teachings of the ancient Greek philosopher Zeno

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "stoicism":
   acceptance, ataraxia, ataraxy, austerity, backbone, bovinity, calm,
   calmness, coolness, dispassion, dispassionateness, dullness,
   easy temper, endurance, even temper, fatalism, forbearance,
   forbearing, forbearingness, fortitude, good temper, grit, guts,
   impassiveness, impassivity, imperturbability, imperturbableness,
   indifference, indulgence, inexcitability, inexcitableness,
   inirritability, insensibility, lenience, leniency, long-sufferance,
   long-suffering, longanimity, patience, patience of Job,
   patientness, perseverance, phlegm, pluck, resignation, sand,
   self-control, self-possession, smooth temper, steadiness,
   stolidity, sufferance, sweet reasonableness, tolerance, toleration,
   unirritableness, unnervousness, unpassionateness, unresponsiveness,
   waiting game, waiting it out



Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "Stoicism":
   Aristotelian philosophy, Aristotelianism, Christian ethics,
   Encratism, Epicureanism, Friday, Lenten fare, Peripatetic school,
   Peripateticism, Platonic philosophy, Platonism, Pythagoreanism,
   Pythagorism, Rechabitism, Shakerism, Spartan fare,
   Stoic philosophy, abstainment, abstemiousness, abstention,
   abstinence, altruistic ethics, aretaics, asceticism, avoidance,
   banyan day, casuistry, categorical imperative, celibacy, chastity,
   comparative ethics, continence, deontology, egoistic ethics,
   empiricism, eschewal, ethical formalism, ethical philosophy,
   ethology, ethonomics, eudaemonics, evolutionism, fast, fish day,
   fruitarianism, golden rule, gymnosophy, hedonism, intuitionism,
   moral philosophy, nephalism, perfectionism, plain living,
   refraining, refrainment, sexual abstinence, simple diet,
   situation ethics, spare diet, teetotalism, the pledge,
   total abstinence, utilitarianism, vegetarianism