dike (n.) Look up dike at Dictionary.com
Old English dic "trench, ditch; an earthwork with a trench; moat," from Proto-Germanic *dik- (source also of Old Norse diki "ditch, fishpond," Old Frisian dik "mound, dam," Middle Dutch dijc "mound, dam, pool," Dutch dijk "dam," German Deich "embankment"), from PIE root *dhigw- "to pierce; to fix, fasten" (see fix (v.)).

At first "an excavation," later applied to the resulting earth mound (late 15c.); a sense development paralleled by cognate forms in many languages. This is the northern variant of the word that in the south of England yielded ditch (n.).