1. with no one else present; alone (of two or more people). Must one sit by oneself or may one join another group?One just hates eating by oneself, doesn't one?
2. with the help of no one else. One is expected to do it by oneself.Can one do this by oneself?
by oneself
Alone, unaccompanied; also, unassisted. For example, She enjoyed being by herself much of the time, or Brian can pick up his toys by himself. [c. a.d. 1000]