The Collaborative International Dictionary of English v.0.48:

Thrice \Thrice\ (thr[imac]s), adv. [OE. thries; thrie thrice
   (AS. [thorn]riga, [thorn]riwa) + -s, the adverbal suffix. See
   Three, and -wards.]
   1. Three times. "Thrice in vain." --Spenser.
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            Verily I say unto thee. That this night, before the
            cock crow, thou shalt deny me thrice. --Matt. xxvi.
                                                  34.
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   2. In a threefold manner or degree; repeatedly; very.
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            Thrice noble lord, let me entreat of you
            To pardon me.                         --Shak.
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            Thrice is he armed that hath his quarrel just.
                                                  --Shak.
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   Note: Thrice is often used, generally with an intensive
         force, to form compounds which are usually of obvious
         meaning; as, in thrice-blessed, thrice-favored,
         thrice-hallowed, thrice-happy, thrice-told, and the
         like.
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WordNet (r) 3.0 (2006):

thrice
    adv 1: three times; "I called you thrice last night"