The Collaborative International Dictionary of English v.0.48:

Rudiment \Ru"di*ment\ (r[udd]"d[i^]*ment), n. [L. rudimentum,
   fr. rudis unwrought, ignorant, rude: cf. F. rudiment. See
   Rude.]
   1. That which is unformed or undeveloped; the principle which
      lies at the bottom of any development; an unfinished
      beginning.
      [1913 Webster]

            but I will bring thee where thou soon shalt quit
            Those rudiments, and see before thine eyes
            The monarchies of the earth.          --Milton.
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            the single leaf is the rudiment of beauty in
            landscape.                            --I. Taylor.
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   2. Hence, an element or first principle of any art or
      science; a beginning of any knowledge; a first step.
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            This boy is forest-born,
            And hath been tutored in the rudiments
            of many desperate studies.            --Shak.
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            There he shall first lay down the rudiments
            Of his great warfare.                 --Milton.
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   3. (Biol.) An imperfect organ or part, or one which is never
      developed.
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The Collaborative International Dictionary of English v.0.48:

Rudiment \Ru"di*ment\, v. t.
   To furnish with first principles or rules; to insrtuct in the
   rudiments. --Gayton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rudiment
    n 1: the elementary stages of any subject (usually plural); "he
         mastered only the rudiments of geometry" [syn: rudiment,
         first rudiment, first principle, alphabet, ABC,
         ABC's, ABCs]
    2: the remains of a body part that was functional at an earlier
       stage of life; "Meckel's diverticulum is the rudiment of the
       embryonic yolk sac"