The Collaborative International Dictionary of English v.0.48:

Protector \Pro*tect"or\, n. [L.: cf. F. protecteur.]
   1. One who, or that which, defends or shields from injury,
      evil, oppression, etc.; a defender; a guardian; a patron.
      [1913 Webster]

            For the world's protector shall be known. --Waller.
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   2. (Eng. Hist.) One having the care of the kingdom during the
      king's minority; a regent.
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            Is it concluded he shall be protector ! --Shak.
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   3. (R. C. Ch.) A cardinal, from one of the more considerable
      Roman Catholic nations, who looks after the interests of
      his people at Rome; also, a cardinal who has the same
      relation to a college, religious order, etc.
      [1913 Webster]

   Lord Protector (Eng. Hist.), the title of Oliver Cromwell
      as supreme governor of the British Commonwealth
      (1653-1658).
      [1913 Webster]

WordNet (r) 3.0 (2006):

protector
    n 1: a person who cares for persons or property [syn:
         defender, guardian, protector, shielder]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "protector":
   advocate, apologist, benefactor, benefactress, bodyguard, champion,
   defender, guard, guardian angel, paladin, patron, patroness,
   pillar, prince regent, protectress, queen regent, regent, rock,
   safekeeper, supporter, tower, tower of strength, upholder,
   vindicator