From Wiktionary, the free dictionary
다 (-da, declarative suffix) + 하 (ha-, “to say”) + 면 (-myeon, “if”): "if one says that..."
다 하면 • (-da ha-myeon)
- if... always; expresses the inevitable, and usually quickly ensuing, result of a hypothetical.
아기는 배고프다 하면 운다.- Agi-neun baegopeu-da hamyeon unda.
- When babies are hungry, they can't help but cry.
그 명장은 싸운다 하면 이겼다.- Geu myeongjang-eun ssaun-da hamyeon igyeotda.
- That famed general was always victorious whenever he fought.
