once

一次；曾经英释中释advon one occasion only

一旦英释中释conjfrom the time when something happens

一次，一回英释中释nfrom the time when something happens

1 I’ve only met her once..我只见过她一面。

2 Paul’s been to Wexford once before..保罗曾去过韦克斯福德一次。