The Collaborative International Dictionary of English v.0.48:

Lightly \Light"ly\, adv.
   1. With little weight; with little force; as, to tread
      lightly; to press lightly.
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            Yet shall thy grave with rising flowers be drest,
            And the green turf lie lightly on thy breast.
                                                  --Pope.
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            Him thus intent Ithuriel with his spear
            Touched lightly.                      --Milton.
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   2. Swiftly; nimbly; with agility.
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            So mikle was that barge, it might not lightly sail.
                                                  --R. of
                                                  Brunne.
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            Watch what thou seest and lightly bring me word.
                                                  --Tennyson.
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   3. Without deep impression.
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            The soft ideas of the cheerful note,
            Lightly received, were easily forgot. --Prior.
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   4. In a small degree; slightly; not severely.
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            At the first he lightly afflicted the land of
            Zebulun . . . and afterward did more grievously
            afflict her.                          --Is. ix. 1.
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   5. With little effort or difficulty; easily; readily.
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            That lightly come, shall lightly go.  --Old Proverb.
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            They come lightly by the malt, and need not spare
            it.                                   --Sir W.
                                                  Scott.
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   6. Without reason, or for reasons of little weight.
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            Flatter not the rich, neither do thou willingly or
            lightly appear before great personages. --Jer.
                                                  Taylor.
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   7. Commonly; usually. [Obs.] --Bp. Fisher.
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            The great thieves of a state are lightly the
            officers of the crown.                --B. Jonson.
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   8. Without dejection; cheerfully. "Seeming to bear it
      lightly." --Shak.
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   9. Without heed or care; with levity; gayly; airily.
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            Matrimony . . . is not by any to be enterprised, nor
            taken in hand, unadvisedly, lightly, or wantonly.
                                                  --Book of
                                                  Common Prayer
                                                  [Eng. Ed.].
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   10. Not chastely; wantonly. --Swift.
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WordNet (r) 3.0 (2006):

lightly
    adv 1: without good reason; "one cannot say such things lightly"
    2: with few burdens; "experienced travellers travel light" [syn:
       lightly, light]
    3: with little weight or force; "she kissed him lightly on the
       forehead" [syn: lightly, softly, gently]
    4: indulging with temperance; "we eat lightly in the morning"
       [ant: hard, heavily, intemperately]
    5: with indifference or without dejection; "he took it lightly"
    6: in a small quantity or extent; "spread the margarine thinly
       over the meat"; "apply paint lightly" [syn: thinly,
       lightly] [ant: thickly]
    7: to a slight degree; "her speech is only lightly accented"