Alone

google

ref

Middle English: from all + one.

wiktionary

ref

From Middle English allone, from earlier all oon(“alone”, literally “all one”), contracted from the Old English phrase eall ān(“entirely alone, solitary, single”), equivalent to al-(“all”) +‎ one. Cognate with Scots alane(“alone”), Saterland Frisian alleene(“alone”), West Frisian allinne(“alone”), Dutch alleen(“alone”), Low German alleen(“alone”), German allein(“alone”), Danish alene(“alone”), Swedish allena(“alone”). More at all and one. Regarding the different phonological development of alone and one, see the note in one.

etymonline

ref

alone (adj., adv.)

"unaccompanied, solitary; without companions, solitary," c. 1300 contraction of all ane, from Old English all ana "unaccompanied, all by oneself," literally "wholly oneself," from all "all, wholly" (see all) + an "one" (see one). It preserves the old pronunciation of one. Similar compounds are found in German (allein) and Dutch (alleen). Sense of "and nothing else" ("Man shall not live on bread alone") is from c. 1200. Related: Aloneness. Adverbial alonely seems to be obsolete since 17c.