touchdown

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Football An act of carrying, receiving, or gaining possession of the ball across the opponent's goal line for a score of six points.
• noun The contact, or moment of contact, of a landing aircraft or spacecraft with the landing surface.

from The Century Dictionary.

• noun In foot-ball, the touching of the ball to the ground by a player behind his opponent's goal; the play by which this is done.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Football) The act of touching the football down behind the opponents' goal; also the score (6 points) resulting from such a play.
• noun See under Safety.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun American football, Canadian football A six-point score occurring when the ball enters possession of a team's player in the opponent's end zone. Analogous to a try in rugby.
• noun aviation The moment when an aircraft makes first or final contact with the ground during a landing.
• noun rugby A try

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb come or bring (a plane) to a landing
• noun a landing (as the wheels touch the landing field); especially of airplanes
• noun a score in American football; being in possession of the ball across the opponents' goal line