To bewail something is to say out loud, at length, how sad or sorry you are about it. The key is that bewailing is audible and public: it is not quiet private sadness but complaining, lamenting, going on about it. It is a formal and literary verb — you meet it in the Bible, in Shakespeare, in old poetry, where people bewail their fate, bewail the death of a king, bewail their sins. In modern English it survives mostly in writing and in a slightly amused, ironic way: 'columnists bewailing the decline of the English language', 'he bewailed the state of the roads'. That ironic use is worth noticing, because it quietly suggests the complaining is a bit much — that the speaker is being dramatic about something not worth it. It is always transitive: you bewail something (bewail his death, bewail the loss, bewail the fact that...). You cannot just 'bewail' with nothing after it. Compare the near neighbours: 'lament' is the standard formal word and slightly more dignified; 'mourn' is about grief for a death and can be silent; 'wail' on its own is the loud crying sound; 'bemoan' is very close to bewail and rather more common today. If a student wants one of these for ordinary use, bemoan or complain about is the safer choice — bewail sounds like a costume.

哀嘆、悲嘆、訴苦（把難過大聲說出來，帶抱怨意味）。文言、書面用語，現代英文多半帶點調侃語氣，暗示對方「講得太誇張了」。日常想說「抱怨」用 complain about 或 bemoan 就好。