Dictionary.net

• congenital disorder consisting of an inability to digest milk and milk products; absence or deficiency of lactase results in an inability to hydrolyze lactose

2006 - WordNet 3.0
By Princeton University

• congenital disorder consisting of an inability to digest milk and milk products; absence or deficiency of lactase results in an inability to hydrolyze lactose

2011 - English Dictionary Database
By DataStellar Co., Ltd