The Collaborative International Dictionary of English v.0.48:

Augment \Aug*ment"\, v. t. [imp. & p. p. Augmented; p. pr. &
   vb. n. Augmenting.] [L. augmentare, fr. augmentum an
   increase, fr. augere to increase; perh. akin to Gr. ?, ?, E.
   wax, v., and eke, v.: cf. F. augmenter.]
   1. To enlarge or increase in size, amount, or degree; to
      swell; to make bigger; as, to augment an army by
      re["e]forcements; rain augments a stream; impatience
      augments an evil.
      [1913 Webster]

            But their spite still serves
            His glory to augment.                 --Milton.
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   2. (Gram.) To add an augment to.
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The Collaborative International Dictionary of English v.0.48:

Augment \Aug*ment"\, v. i.
   To increase; to grow larger, stronger, or more intense; as, a
   stream augments by rain.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Augment \Aug"ment\, n. [L. augmentum: cf. F. augment.]
   1. Enlargement by addition; increase.
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   2. (Gram.) A vowel prefixed, or a lengthening of the initial
      vowel, to mark past time, as in Greek and Sanskrit verbs.
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   Note: In Greek, the syllabic augment is a prefixed ?, forming
         an intial syllable; the temporal augment is an increase
         of the quantity (time) of an initial vowel, as by
         changing ? to ?.
         [1913 Webster]

WordNet (r) 3.0 (2006):

augment
    v 1: enlarge or increase; "The recent speech of the president
         augmented tensions in the Near East"
    2: grow or intensify; "The pressure augmented"