ことごとく is a formal, literary adverb used to express that something applies to every member of a set, leaving nothing out. It carries a sense of totality and often has a negative or dramatic nuance, such as when describing failures, losses, or destruction. In conversation, it sounds stiff and bookish; you'll mostly encounter it in written narratives, news reports, or formal speeches.

When used with a noun, it often appears as 'Nはことごとく' or 'Nをことごとく', where N is a plural or collective noun. For example, '計画はことごとく失敗した' means 'the plans failed completely, every one of them.' When used with a verb, it often comes right before the verb, as in 'ことごとく否定された' (were all denied).

A common alternative in everyday speech is '全部' (all) or 'すっかり' (completely), but those lack the emphatic, sweeping tone of ことごとく. Using ことごとく in casual conversation can sound overly dramatic or even humorous, so be aware of the register.