n. 1 dike: 7. a. A ridge, embankment, long mound, or dam, thrown up to resist the encroachments of the sea, or to prevent low-lying lands from being flooded by seas, rivers, or streams. (Oxford English Dictionary)
n. 2 dyke. Of obscure origin. A lesbian; a masculine woman. Also attrib.
1942 BERREY & VAN DEN BARK Amer. Thes. Slang §405/3 Masculine woman,..dike, dyke.
The spelling DIKE is the proper etymological spelling for the ditch. The spelling DYKE is useful to make the difference clear.
John: "Dude how do you cut a wire with a rug muncher?"
Rick: **smack** "A dyke is a also a wire cutters you fuckin deusch bag!"