at the bottom of something—
1. in the lowest part outside smth.:
- I stood there at the bottom of the steps.
2. in the part farthest from the front:
- The poor relations were seated at the bottom of the long table.
3. being the real cause of smth. undesirable:
- Greed lies at the bottom of our ecological predicament.
in the bottom of something—in the lowest part inside smth.:
- The fish we had caught were flopping about in the bottom of the boat.