Definition of by oneself
1 : without any help from other people I shoveled the driveway by myself. I want you to figure it out by yourself.
2 : with noone or nothing else : alone The grandmother still lives in the house by herself. He went to the store by himself. They toured the city by themselves. The new law will help, but it can't solve the problem (all) by itself.
Seen and Heard
What made you want to look up by oneself? Please tell us where you read or heard it (including the quote, if possible).