by ourselves
by (oneself)
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
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
by ourselves
1. with no one else present; alone. Do we have to sit here by ourselves? Can't we sit with Mary and Max? We like to eat by ourselves, so we can talk about private matters. 2. with the help of no one else. We can do it by ourselves. Can we lift this by ourselves, or do we need some help?
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.