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.
      [1913 Webster]

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.
      [1913 Webster]

   2. (Gram.) A vowel prefixed, or a lengthening of the initial
      vowel, to mark past time, as in Greek and Sanskrit verbs.
      [1913 Webster]

   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]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "augment":
   add to, agent provocateur, aggrandize, aggravate, amplify, annoy,
   bloat, blow up, boost, broaden, build, build up, bulk, bulk out,
   compound, crescendo, deepen, deteriorate, develop, dilate, distend,
   embitter, enhance, enlarge, exacerbate, exalt, exasperate, expand,
   extend, fatten, fill out, fortify, heat up, heighten, hike,
   hike up, hot up, huff, increase, inflate, intensify, irritate,
   jack up, jump up, lengthen, magnify, make acute, make worse,
   manifold, maximize, mount, multiply, parlay, provoke, puff,
   puff up, pump, pump up, put up, pyramid, raise, rarefy, recruit,
   reinforce, rise, sharpen, sour, strengthen, stretch, sufflate,
   supplement, swell, thicken, up, upsurge, wax, widen, worsen