Meaning

adverb from that place or from there

adverb from that circumstance or source; - W.V.Quine

adverb (used to introduce a logical conclusion) from that fact or reason or as a result

originFrom Middle English þennes, from þenne + -es (“adverbial ending”), the former from þanan, þanona, from Proto-West Germanic *þananā. Cognate with Westphalian Low German diëne.

Etymology from Wiktionary, CC BY-SA 3.0