thence (adv.)

late 13c., from Old English þanone, þanon "from that place" + adverbial genitive -es. Old English þanone/þanon is from Proto-Germanic *thanana (source also of Old Saxon thanana, Old Norse þana, Old Frisian thana, Old High German danana, German von dannen), related obscurely to the root of then, and ultimately from PIE demonstrative base *to- (see the). Written with -c- to indicate a voiceless "s" sound. Meaning "from that time" is from late 14c.; sense of "for that reason" is from 1650s. From thence is redundant.

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Definitions of thence from WordNet

thence (adv.)
from that place or from there;
proceeded thence directly to college
flew to Helsinki and thence to Moscow
Synonyms: therefrom
thence (adv.)
from that circumstance or source; "atomic formulas and all compounds thence constructible"- W.V.Quine;
a natural conclusion follows thence
Synonyms: therefrom / thereof
thence (adv.)
(used to introduce a logical conclusion) from that fact or reason or as a result;
we were young and thence optimistic
Synonyms: therefore / hence / thus / so