þ (thorn) is a character from Old English and some Scandinavian scripts. It represents the phonemes. Wiþ = with, þink = think. Thorn can be used for both the voiced and voiceless (voiceless: thin, voiced: that), but ð (eth) can also be used for tge voiced version. Farðer = farther, ðose = those. I quite like both, and the only reason I don’t use them is because I haven’t found a keyboard I can use them with.