English is a mish-mash of many languages, but the two most influential are French (Latin) and Old German (Anglo, Saxon, Jute, etc). Man- as a Latin root usually means "hand." Thus we have the old...
This is a typically Dutch expression. (Een man een man, een woord een woord). If you make a promise, you have to keep it. A good English translation for it is: an honest man is as good as his word.