资料来源 : Webster's Revised Unabridged Dictionary (1913)

Ha-ha \Ha-ha"\, n. [See {Haw-haw}.]
   A sunk fence; a fence, wall, or ditch, not visible till one
   is close upon it. [Written also {haw-haw}.]

资料来源 : WordNet®

ha-ha
     n 1: a loud laugh that sounds like a horse neighing [syn: {hee-haw},
           {horselaugh}, {haw-haw}]
     2: a ditch with one side being a retaining wall; used to divide
        lands without defacing the landscape [syn: {sunk fence}, {haw-haw}]