[1] : The Collaborative International Dictionary of English v.0.48

touchdown \touch"down`\ tu^ch"doun`, n. football
   the act of touching the football down behind the opponents'
   goal; also the score 6 points resulting from such a play.
   1913 webster

   safety touchdown. see under safety.
      1913 webster
see also:
safety touchdown safety 

[2] : WordNet (r) 2.0

touchdown
     n 1: a score in american football; being in possession of the
          ball across the opponents' goal line
     2: a landing as the wheels touch the landing field;
        especially of airplanes

Touchdown >> T Words
Touchdown, definition of term: Touchdown
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