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.
under prep., adv.
Old English under (prep.) "beneath, among, before, in the presence of, in subjection to, under the rule of, by means of," also, as an adverb, "beneath, below, underneath," expressing position with reference to that which is above, from Proto-Germanic *under- (source also of Old Frisian under, Dutch onder, Old High German untar, German unter, Old Norse undir, Gothic undar), from PIE *ndher- "under" (source also of Sanskrit adhah "below;" Avestan athara- "lower;" Latin infernus "lower," infra "below").
Productive as a prefix in Old English, as in German and Scandinavian (often forming words modeled on Latin ones in sub-). Notion of "inferior in rank, position, etc." was present in Old English. With reference to standards, "less than in age, price, value," etc., late 14c. As an adjective, "lower in position; lower in rank or degree" from 13c. Also used in Old English as a preposition meaning "between, among," as still in under these circumstances, etc. (though this may be an entirely separate root; see understand).
Under the weather "indisposed" is from 1810. Under the table is from 1913 in the sense of "very drunk," 1940s in sense of "illegal" (under-board "dishonest" is from c. 1600). To keep something under (one's) hat "secret" is from 1885; to have something under (one's) nose "in plain sight" is from 1540s; to speak under (one's) breath "in a low voice" is attested from 1832.