1.Dyke comes from the
dutch word 'Dijk'. A 'dijk' is an embankment that protects water from entering dry land. Because many parts of Holland lie beneath sea level, holland contains a lot of 'dijken' ( multiple for dijk).
2. There is a myth about a man that used his
finger to hold down a hole in a dijk to save the land behind it.
'Putting a
finger in a dyke' is a sexual term.