therein

The story

1. Proto-Germanic · inherited from*þarin
2. Proto-West Germanic · inherited from*þārin
3. Old English · inherited fromþǣrin
4. Middle English · inherited fromtheryn
5. English todaytherein

From Middle English theryn, ther-inne, þer-in, from Old English þǣrin, þǣrinne, from Proto-West Germanic *þārin, *þārinna, from Proto-Germanic *þarin, *þarinna, equivalent to there + in. Cognate with Saterland Frisian deerin (“therein”), West Frisian dêryn (“therein”), Dutch daarin (“therein”), German Low German daarin (“therein”), German darin, drin (“therein”), Danish deri (“therein”), Swedish däri (“therein”), Icelandic þar í (“therein”).