落空 (luò kōng) is a verb meaning 'to come to nothing' or 'to fail' — especially when hopes, plans, expectations, or efforts do not materialize. Literally, 落 means 'to fall' or 'to land', and 空 means 'empty' or 'void'; together, they evoke the image of something falling into emptiness — suggesting disappointment or unfulfilled intention. It’s commonly used with subjects like plans, hopes, expectations, promises, or attempts.

This word carries a tone of regret or mild disappointment and appears frequently in spoken and written Chinese when describing unrealized outcomes. It’s often paired with nouns such as 希望 (hopes), 计划 (plans), 承诺 (promises), or 努力 (efforts). While not formal or literary per se, it’s more common in mature, natural speech than in very casual slang — and it’s rarely used in isolation; it typically follows the noun it modifies (e.g., 希望落空, 计划落空).