1. Alone. Because there's usually so much going on with the kids, I really enjoy spending a quiet Saturday night by myself.
2. Through one's own efforts alone. You can't move that table all by yourself! Here, let me help you. My little girl loves to get dressed by herself, so tutus and cowboy boots have become the norm around here.
See also: by
1. with help from no one else. Do you think they can do it by themselves? Mike and Max cannot lift the piano by themselves.
2. with no one else present; alone (of two or more people). They are sitting there by themselves. Let's sit with them. They enjoy spending the evening at home by themselves.