by oneself
by oneself {adv. phr.}
1. Without any others around; separate from others; alone.
The house stood by itself on a hill.
Tom liked to go walking by himself.
Betty felt very sad and lonely by herself.
2. Without the help of anyone else; by your own work only.
John built a flying model airplane by himself.
Lois cleaned the house all by herself.
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Source: A Dictionary of American Idioms