The Collaborative International Dictionary of English v.0.48:

Ludicrous \Lu"di*crous\, a. [L. ludicrus, or ludicer, from ludus
   play, sport, fr. ludere to play.]
   1. Adapted to excite laughter, without scorn or contempt;
      sportive. --Broome.
      [1913 Webster]

            A chapter upon German rhetoric would be in the same
            ludicrous predicament as Van Troil's chapter on the
            snakes of Iceland, which delivers its business in
            one summary sentence, announcing, that snakes in
            Iceland -- there are none.            --De Quincey.

   2. Ridiculously absurd.
      [PJC]

   Syn: Laughable; sportive; burlesque; comic; droll;
        ridiculous.

   Usage: Ludicrous, Laughable, Ridiculous. We speak of a
          thing as ludicrous when it tends to produce laughter;
          as laughable when the impression is somewhat stronger;
          as ridiculous when more or less contempt is mingled
          with the merriment created. -- Lu"di*crous*ly, adv.
          -- Lu"di*crous*ness, n.
          [1913 Webster]

WordNet (r) 3.0 (2006):

ludicrously
    adv 1: so as to arouse or deserve laughter; "her income was
           laughably small, but she managed to live well" [syn:
           laughably, ridiculously, ludicrously,
           preposterously]