thus: [OE] Thus is something of a mystery word. It presumably belongs to the family of words (that, there, etc) that go back to the prehistoric Germanic demonstrative base *tha-, but how its fits into the family tree is not clear. Its only close relative is Dutch dus ‘thus’. [thus etymology, thus origin, 英语词源]
Old English þus "in this way, as follows," related to þæt "that" and this; from Proto-Germanic *thus- (cognates: Old Saxon and Old Frisian thus, Middle Dutch and Dutch dus), from PIE *to-.