otherwise adv.

Old English oþer "second, the second of two; additional, further" (adj.), also as a pronoun, "one of the two; a different person or thing from the one in view," from Proto-Germanic *anthera- (source also of Old Saxon athar, Old Frisian other, Old Norse annarr, Middle Dutch and Dutch ander, Old High German andar, German ander, Gothic anþar "second, other").

These are from PIE *an-tero-(source of Lithuanian antras, Old Prussian anters "other, second), which is perhaps a variant of *al-tero- "the other of two" (source of Latin alter), from root *al- "beyond" + adjectival comparative suffix *-tero-.  Or the first element might be the pronoun *eno-, *ono- [Boutkan]. The Old English, Old Saxon, and Old Frisian forms show "a normal loss of n before fricatives" [Barnhart].

The sense of "second" was detached from this word in English (which now uses second (adj.), which is from Latin) and German (zweiter, from zwei "two") to avoid ambiguity. In Scandinavian, however, the second floor is still the "other" floor (Swedish andra, Danish anden). Also compare Old English oþergeara "next year."

As an adverb, "secondly" (late Old English); "otherwise" (c. 1200); "in addition" (mid-14c.).

The other woman "a woman with whom a man begins a love affair while he is already committed" is from 1855. The other day originally (late Old English) was "the next day;" later (c. 1300) "yesterday;" and now, loosely, "a day or two ago" (early 15c.). OED notes that the other place was euphemistic for Hell or "Oxford as regarded in Cambridge (and vice versa)." Phrase other half in reference to either the poor or the rich, is recorded from c. 1600.

La moitié du monde ne sçayt comment l'aultre vit. [Rabelais, "Pantagruel," 1532]

Halfe the world knowes not how the other halfe li[v]es. [George Herbert, "Outlandish Proverbs," 1640]

"way of proceeding, manner," Old English wise "way, fashion, custom, habit, manner; condition, state, circumstance," from Proto-Germanic *wison "appearance, form, manner" (see wise (adj.)). Compare Old Saxon wisa, Old Frisian wis, Danish vis, Middle Dutch wise, Dutch wijs, Old High German wisa, German Weise "way, manner." Most common in English now as a word-forming element (as in likewise, clockwise); the adverbial -wise has been used thus since Old English. For sense evolution from "to see" to "way of proceeding," compare cognate Greek eidos "form, shape, kind," also "course of action." Ground sense is "to see/know the way."