alone:  Although partly disguised by its pronunciation, alone is in fact simply a compound of all and one (whose /wun/ pronunciation began to develop around the 15th century). In Old English it was a completely separate phrase, all āna, literally ‘completely by oneself’, but by the 13th century this had coalesced into a single word. Loss of its initial ain the 14th century gave rise to the adjective lone. => all, lone, one
c. 1300 contraction of all ane, from Old English all ana "unaccompanied, all by oneself," from all "all, wholly" (see all) + an "one" (see one). Similar compounds are found in German (allein) and Dutch (alleen).
1. If you're lonely when you're alone, you're in bad company.--Jean Paul Sartre
2. Don't leave a child alone in a room with an open fire.
3. He knew when to leave well alone and when to interfere.
4. He had always been an outcast, unwanted and alone.
5. He was working alone and did not have an accomplice.