さようなら。

Sayōnara.

Goodbye.

Word for word

“If it must be so…”

Politeness: Neutral

Fixed expression that suits almost everyone, with no politeness marker to adjust.

When you would say it

A formal or final farewell: school, ending a trip, a long separation.

Worth knowing

Rarely used among adults day to day. Colleagues say お先に失礼します or お疲れ様でした instead.