The Collaborative International Dictionary of English v.0.48:

Imagine \Im*ag"ine\, v. t. [imp. & p. p. Imagined; p. pr. &
   vb. n. Imagining.] [F. imaginer, L. imaginari, p. p.
   imaginatus, fr. imago image. See Image.]
   1. To form in the mind a notion or idea of; to form a mental
      image of; to conceive; to produce by the imagination.
      [1913 Webster]

            In the night, imagining some fear,
            How easy is a bush supposed a bear!   --Shak.
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   2. To contrive in purpose; to scheme; to devise; to compass;
      to purpose. See Compass, v. t., 5.
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            How long will ye imagine mischief against a man?
                                                  --Ps. lxii. 3.
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   3. To represent to one's self; to think; to believe. --Shak.

   Syn: To fancy; conceive; apprehend; think; believe; suppose;
        opine; deem; plan; scheme; devise.
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The Collaborative International Dictionary of English v.0.48:

Imagine \Im*ag"ine\, v. i.
   1. To form images or conceptions; to conceive; to devise.
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   2. To think; to suppose.
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            My sister is not so defenseless left
            As you imagine.                       --Milton.
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WordNet (r) 3.0 (2006):

imagine
    v 1: form a mental image of something that is not present or
         that is not the case; "Can you conceive of him as the
         president?" [syn: imagine, conceive of, ideate,
         envisage]
    2: expect, believe, or suppose; "I imagine she earned a lot of
       money with her new novel"; "I thought to find her in a bad
       state"; "he didn't think to find her in the kitchen"; "I
       guess she is angry at me for standing her up" [syn: think,
       opine, suppose, imagine, reckon, guess]