Old English dic "trench, ditch; an earthwork with a trench; moat," from Proto-Germanic *dik- (cf. 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 *dheigw- "to pierce, fasten" (cf. Sanskrit dehi- "wall," Old Persian dida "wall, stronghold, fortress," Persian diz).
At first "an excavation," later (late 15c.) applied to the resulting earth mound; a sense development paralleled by cognate forms in many other languages. This is the northern variant of the word that in the south of England yielded ditch (n.).
Resembling or having the nature of an aggressive lesbian: doing calisthenics with the dikey-looking brunette (1960s+)