elseyoudaoicibaDictYouDict[else 词源字典]
else: [OE] Else shares its sense of ‘otherness’ with related words in other parts of the Indo- European language family. It comes ultimately from the base *al-, which also produced Latin alter ‘other’ (source of English alter) and alius ‘other’ (source of English alibi and alien) and Greek állos ‘other’ (source of the prefix allo- in such English words as allopathy, allophone, and allotropy). Its Germanic descendant was *aljo- ‘other’, whose genitive neuter case *aljaz, used adverbially, eventually became English else.
=> alibi, alien, alter[else etymology, else origin, 英语词源]
else (adv.)youdaoicibaDictYouDict
Old English elles "in another manner, other, otherwise, besides, different," from Proto-Germanic *aljaz (cognates: Gothic aljis "other," Old High German eli-lenti, Old English el-lende, both meaning "in a foreign land;" see also Alsace), an adverbial genitive of the neuter of PIE root *al- (1) "beyond" (cognates: Greek allos "other," Latin alius; see alias (adv.)). As a quasi-adjective, synonymous with other, from 1660s; the nuances of usage are often arbitrary.

Productive of a number of handy compounds that somehow never got traction or have been suffered to fall from use: elsehow (1660s) "somehow or other;" elsewards (adv.), 1882, "somewhere else;" Old English elsewhat (pron.) " something else, anything else;" elsewhen (adv.), early 15c., "at another time; elsewhence (c. 1600); elsewho (1540s). Among the survivors are elsewhere, elsewise. Menacing or else, with omitted but implied threat, is from 1833.