herein adv.

Old English her "in this place, where one puts himself; at this time, toward this place," from Proto-Germanic pronominal stem *hi- (from PIE *ki- "this;" see he) + adverbial suffix -r. Cognate with Old Saxon her, Old Norse, Gothic her, Swedish här, Middle Dutch, Dutch hier, Old High German hiar, German hier.

As the answer to a call, in Old English. Right here "on the spot" is from c. 1200. Here and there "in various places" is from c. 1300. Phrase here today and gone tomorrow first recorded 1680s in writings of Aphra Behn. Here's to _____ as a toast is from 1590s, probably short for here's health to _____. Emphatic this here (adv.) is attested from mid-15c.; colloquially, this here as an adjective is attested from 1762. To be neither here nor there "of no consequence" is attested from 1580s. Here we go again as a sort of verbal rolling of the eyes is attested from 1950.

As a noun, "this place, the present" from c. 1600. Noun phrase here-and-now "this present life" is from 1829.

a Middle English merger of Old English in (prep.) "in, into, upon, on, at, among; about, during;" and Old English inne (adv.) "within, inside," from Proto-Germanic *in (source also of Old Frisian, Dutch, German, Gothic in, Old Norse i), from PIE root *en "in." The simpler form took on both senses in Middle English.

Sense distinction between in and on is from later Middle English, and nuances in use of in and at still distinguish British and American English (in school/at school). Sometimes in Middle English shortened to i.

The noun sense of "influence, access (to power or authorities)," as in have an in with, is first recorded 1929 in American English. to be in for it "certain to meet with something unpleasant" is from 1690s. To be in with "on friendly terms with" is from 1670s. Ins and outs "intricacies, complications of an action or course" is from 1660s. In-and-out (n.) "copulation" is attested from 1610s.