Source : Webster's Revised Unabridged Dictionary (1913)

Laugh \Laugh\, v. i. [imp. & p. p. {Laughed}; p. pr. & vb. n.
   {Laughing}.] [OE. laughen, laghen, lauhen, AS. hlehhan,
   hlihhan, hlyhhan, hliehhan; akin to OS. hlahan, D. & G.
   lachen, OHG. hlahhan, lahhan, lahh?n, Icel. hl[ae]ja. Dan.
   lee, Sw. le, Goth. hlahjan; perh. of imitative origin.]
   1. To show mirth, satisfaction, or derision, by peculiar
      movement of the muscles of the face, particularly of the
      mouth, causing a lighting up of the face and eyes, and
      usually accompanied by the emission of explosive or
      chuckling sounds from the chest and throat; to indulge in
      laughter.

            Queen Hecuba laughed that her eyes ran o'er. --Shak.

            He laugheth that winneth.             --Heywood's
                                                  Prov.

   2. Fig.: To be or appear gay, cheerful, pleasant, mirthful,
      lively, or brilliant; to sparkle; to sport.

            Then laughs the childish year, with flowerets
            crowned.                              --Dryden.

            In Folly's cup still laughs the bubble Joy. --Pope.

   {To laugh at}, to make an object of laughter or ridicule; to
      make fun of; to deride.

            No wit to flatter left of all his store, No fool to
            laugh at, which he valued more.       --Pope.

   {To laugh in the sleeve}

Laughing \Laugh"ing\, a. & n.
   from {Laugh}, v. i.

   {Laughing falcon} (Zo["o]l.), a South American hawk
      ({Herpetotheres cachinnans}); -- so called from its notes,
      which resemble a shrill laughing.

   {Laughing gas} (Chem.), hyponitrous oxide, or protoxide of
      nitrogen

Source : WordNet®

laughing
     adj : showing or feeling mirth or pleasure or happiness; "laughing
           children" [syn: {laughing(a)}, {riant}]