A mahjong hand containing two identical sequences (same numbers and same suit).
See also: 一盃口 (イーペーコー)
Pure double chow is a hand that contains two identical sequences of the same suit.
一盃口 is the Japanese term for the same mahjong hand; 一色同順 is an alternative, less common name.
Compound of 一色 (one suit) and 同順 (same sequence), describing the mahjong hand pattern.