Old English hider, from Proto-Germanic *hideran (cf. Old Norse heðra "here," Gothic hidre "hither"), from Germanic demonstrative base *hi- (cf. he, here). Spelling change from -d- to -th- is the same evolution seen in father. Relation to here is the same as that of thither to there.
Also, hither and yon. Here and there, as in I've been wandering about, hither and thither, or Ruth went hither and yon, searching for her sister. These old words for “here” and “there” are rarely heard outside these expressions, which themselves may be dying out. [c. a.d. 725]