good-by

She waved her hand as a final good-by before the train departed.

用法提示：这里good-by作为名词，指告别这一行为或话语。

We exchanged tearful good-bys at the airport gate.

用法提示：复数形式good-bys表示多次或多人之间的告别。

His good-by was brief but heartfelt, leaving everyone touched.

用法提示：good-by作为主语，表示告别的话语或举动。