Dictionary.net

• the position of the football player in the backfield who directs the offensive play of his team; "quarterback is the most important position on the team"

2006 - WordNet 3.0
By Princeton University

• the position of the football player in the backfield who directs the offensive play of his team; "quarterback is the most important position on the team"

2011 - English Dictionary Database
By DataStellar Co., Ltd