The Collaborative International Dictionary
Marchet \Mar"chet\, Merchet \Mer"chet\, n. [LL. marcheta; of uncertain origin.] In old English and in Scots law, a fine paid to the lord of the soil by a tenant upon the marriage of one the tenant's daughters.
n. (context obsolete English) In Middle Ages England, a fine paid to a lord on a daughter's marriage, in recompense for the loss of a worker.
A merchet was a fine paid on a marriage during the Middle Ages in England. The word derives from the plural form of daughter, merched, in old Welsh. A peasant would pay a merchet to his lord upon the marriage of a woman. The justification for this was that when a woman married, her lord was losing a worker. Usually the bride's father would pay, as buying the right to give his daughter away.
There is an unsubstantiated theory that relates this fine to droit du seigneur