The Collaborative International Dictionary of English v.0.48:

Mastery \Mas"ter*y\, n.; pl. Masteries. [OF. maistrie.]
   [1913 Webster]
   1. The position or authority of a master; dominion; command;
      supremacy; superiority.
      [1913 Webster]

            If divided by mountains, they will fight for the
            mastery of the passages of the tops.  --Sir W.
                                                  Raleigh.
      [1913 Webster]

   2. Superiority in war or competition; victory; triumph;
      preeminence.
      [1913 Webster]

            The voice of them that shout for mastery. --Ex.
                                                  xxxii. 18.
      [1913 Webster]

            Every man that striveth for the mastery is temperate
            in all things.                        --1 Cor. ix.
                                                  25.
      [1913 Webster]

            O, but to have gulled him
            Had been a mastery.                   --B. Jonson.
      [1913 Webster]

   3. Contest for superiority. [Obs.] --Holland.
      [1913 Webster]

   4. A masterly operation; a feat. [Obs.]
      [1913 Webster]

            I will do a maistrie ere I go.        --Chaucer.
      [1913 Webster]

   5. Specifically, the philosopher's stone. [Obs.]
      [1913 Webster]

   6. The act process of mastering; the state of having
      mastered.
      [1913 Webster]

            He could attain to a mastery in all languages.
                                                  --Tillotson.
      [1913 Webster]

            The learning and mastery of a tongue, being
            unpleasant in itself, should not be cumbered with
            other difficulties.                   --Locke.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mastery
    n 1: great skillfulness and knowledge of some subject or
         activity; "a good command of French" [syn: command,
         control, mastery]
    2: power to dominate or defeat; "mastery of the seas" [syn:
       domination, mastery, supremacy]
    3: the act of mastering or subordinating someone [syn:
       mastery, subordination]

Moby Thesaurus II by Grady Ward, 1.0:

315 Moby Thesaurus words for "mastery":
   Cadmean victory, KO, Pyrrhic victory, Waterloo, ability, acme,
   address, adeptness, adroitness, aedileship, airmanship,
   apprehension, archbishopric, archiepiscopacy, archiepiscopate,
   aristocracy, artfulness, artisanship, artistry, ascendancy,
   authority, authorization, be-all and end-all, beating, bishopric,
   blue ribbon, bravura, brilliance, capability, capacity,
   chairmanship, championship, chancellery, chancellorate,
   chancellorship, charisma, charm, chiefery, chiefry, chieftaincy,
   chieftainry, chieftainship, clairvoyance, claws, cleverness, clout,
   clutches, collapse, command, competence, competency, comprehension,
   conception, conceptualization, condition, conquering, conquest,
   consequence, consulate, consulship, control, coordination, craft,
   craftsmanship, crash, credit, cunning, deanery, deathblow, debacle,
   defeat, deftness, destruction, dexterity, dexterousness,
   dextrousness, dictatorship, dictature, diplomacy, directorship,
   dominance, domination, dominion, downfall, drubbing, easy victory,
   effect, effectiveness, efficiency, eminence, emirate, enchantment,
   episcopacy, esteem, expertise, expertism, expertness, facility,
   failure, fall, favor, finesse, first place, first prize, fitness,
   fittedness, force, foreknowledge, good feeling, governorship,
   grace, grand slam, grasp, grip, gripe, hand, handiness, hands,
   headship, hegemony, height, helm, hiding, hierarchy, highest, hold,
   horsemanship, ideation, imperium, importance, incidental power,
   influence, influentiality, ingeniousness, ingenuity, insinuation,
   intellection, intelligence, iron hand, jurisdiction, kingship,
   knack, knockout, know-how, lambasting, landslide,
   landslide victory, lathering, leadership, leverage, licking,
   lordship, magistracy, magistrateship, magistrature, magnetism,
   management, marksmanship, masterdom, mastership, maturity, maximum,
   mayoralty, mayorship, mental grasp, metropolitanate,
   metropolitanship, might, moment, moral victory, most,
   ne plus ultra, new high, nobility, overcoming, overthrow, overturn,
   palms, papacy, paramountcy, pashadom, pashalic, patriarchate,
   patriarchy, personality, persuasion, picnic, pontificality,
   pontificate, popedom, popehood, popeship, potency, power,
   practical ability, precognition, predominance, prefectship,
   prefecture, prehension, premiership, preparedness, preponderance,
   presidency, presidentship, pressure, prestige, primacy,
   prime-ministership, prime-ministry, princedom, princeship,
   principality, proconsulate, proconsulship, proficiency,
   protectorate, protectorship, provostry, provostship, prowess,
   purchase, pushover, qualification, quickness, quietus, readiness,
   record, rectorate, rectorship, regency, regentship, reign,
   reins of government, repute, resource, resourcefulness, ripeness,
   ruin, rule, ruling class, runaway victory, savoir-faire, savvy,
   say, seamanship, seasoning, seigniory, seneschalship, seneschalsy,
   sheikhdom, sheriffalty, sheriffcy, sheriffdom, shrievalty, skill,
   skillfulness, smash, sovereignty, strings, style, suasion, subdual,
   subduing, subjugation, subtle influence, success, suggestion,
   suitability, suitableness, suitedness, supervisorship, supremacy,
   suzerainship, suzerainty, swag, sway, tact, tactfulness, talons,
   technical brilliance, technical mastery, technical skill,
   technique, tempering, thrashing, timing, top spot, total victory,
   tribunate, trim, trimming, triumph, trouncing, understanding,
   undoing, upper hand, vanquishment, victory, virtuosity, vizierate,
   viziership, walkaway, walkover, weight, whip hand, whipping, win,
   winning, winning streak, wisdom, wit, wizardry, workmanship,
   zenith