Source : Webster's Revised Unabridged Dictionary (1913)

Flunk \Flunk\, v. i. [imp. & p. p. {Flunked}; p. pr. & vb. n.
   {Flunking}.] [Cf. {Funk}.]
   To fail, as on a lesson; to back out, as from an undertaking,
   through fear.

Flunk \Flunk\, v. t.
   To fail in; to shirk, as a task or duty. [Colloq. U.S.]

Flunk \Flunk\, n.
   A failure or backing out; specifically (College cant), a
   total failure in a recitation. [U.S.]

Source : WordNet®

flunk
     v : fail to get a passing grade; "She studied hard but failed
         nevertheless"; "Did I fail the test?" [syn: {fail}, {bomb},
          {flush it}] [ant: {pass}]