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myl [Flemish] or mijl [Dutch]

1

A Dutch unit of distance conceptually equal to 1/15 of a degree of latitude, used by navigators. It gradually lengthened as the size of the Earth became known with more precision.

In the 15ᵗʰ century, = 18,930 Amsterdam voet (5,359 meters).

Then changed to = 20,000 Amsterdam voet (5662 meters).

Next = 20,000 Rhenish voet (6,277 meters).

Around 1615 changed to = 22,800 Rhenish voet (7,156 meters) as a result of Snellius' measuring of a degree of latitude as 1900 Rhenish ruthen.

In the early 18ᵗʰ century it was adjusted again to 7,408.8 meters, and was then abandoned in favor of definition 2, below, to correspond to the usage of other nations.

2

A Dutch unit of distance conceptually equal to 1/20th of a degree of latitude.

3

With metrication, it became a name for the kilometer.

for further reading

Herman Wagner.
Zur Geschichte de Seemeile.
Annalen der Hydrographie und Maritimen Meteorologie, vol 41, pages 446-449 (1913).