However / Nevertheless / But
A formal connective used to introduce a contrast. Common in both speech and writing. More formal than pero but very natural in extended conversation.
It's a good offer; however, I need to think about it.
I studied a lot. Nevertheless, the exam was difficult.
—Did you accept it? —Nevertheless, I have my doubts.
I wanted to go, however, I was very tired.
The car is nice; however, it uses a lot of gas.