Source : Webster's Revised Unabridged Dictionary (1913)

Snicker \Snick"er\, n.
   A half suppressed, broken laugh. [Written also {snigger}.]

Snicker \Snick"er\, v. i. [imp. & p. p. {Snickered}; p. pr. &
   vb. n. {Snickering}.] [Cf. D. snikken to sob, to sigh.]
   [Written also {snigger}.]
   1. To laugh slyly; to laugh in one's sleeve.

   2. To laugh with audible catches of voice, as when persons
      attempt to suppress loud laughter.

Source : WordNet®

snicker
     n : a disrespectful laugh [syn: {snort}, {snigger}]

snicker
     v : laugh quietly [syn: {snigger}]