Where does “thi/thī” come from?

thi/thī (Old Frisian) comes from Proto-Germanic þa, from Proto-Indo-European tód, from Proto-Indo-European to-, from Proto-Indo-European só — this; that.

Ancestry of “thi/thī”, step by step

StepLanguageWordMeaning
1Proto-Germanicþa—
2Proto-Indo-Europeantóddemonstrative pronoun; that; it
3Proto-Indo-Europeanto-it; that; the, that
4Proto-Indo-Europeansóthis; that

Words derived from “thi/thī”

Every word from Proto-Indo-European só →Every word from Proto-Indo-European to- →Every word from Proto-Indo-European tód →