Ðð = voiced “th” (“this,” “thus,” “weather”) Þþ = unvoiced “th” (“thing,” “thong,” “with”)

IIRC, these (ðese) letters come from Old English and Old Norse, and were later dropped in favor of “th” for both the voices and unvoiced consonants.

But I’m not an expert. That’s the gist anyway.

Some folks want to bring these letters back. I get it, and I actually like them. But it ain’t gonna happen.

Anyway, “ðey” missed one.