1. Bittersweet | adj. tinged with a feeling of sadness | The ending of the romance movie was bittersweet.
2. Bolster | v. to support, strengthen, or fortify | If we work together, we should be able to lift and then bolster the couch.
3. Boost | n. an increase or growth / v. to increase or make grow | The boost in profits was a welcome change.

Resource: https://blog.prepscholar.com/sat-vocabulary-words