The disciplined student always completes homework on time.

disciplined 是形容词，由动词 discipline（训练、管教）加上后缀 -ed 构成。discipline 本身来自拉丁语 disciplina（教导、纪律），表示通过训练使人遵守规则或养成习惯。disciplined 形容一个人"遵守纪律的、自律的"。