The characters literally combine to mean “joy (乐) not (不) able to (可) support (支)”. The meaning is beautifully direct: the happiness is so intense that one's body is physically unable to support it, leading to uncontrollable laughter, jubilant gestures, or a feeling of being overwhelmed with glee.
乐不可支 is a highly descriptive idiom that captures a very visual and visceral aspect of extreme happiness. While some aspects of Chinese culture value emotional restraint, idioms like this demonstrate a deep appreciation for moments of pure, uninhibited joy. It emphasizes the physical, uncontrollable nature of powerful emotions. A Western cultural comparison might be “doubled over with laughter” or “beside oneself with joy.” However, the Chinese term is unique in its focus on the failure of physical support. While “doubled over” describes a specific action, 乐不可支 describes the underlying state: the joy is a force so strong that the body's structural integrity (its ability to “support” itself) is compromised. This reflects a holistic view where intense emotion and physical response are inextricably linked. This idiom is often used to describe reactions to wonderful news (like a child's success), hilarious situations, or the culmination of a long-awaited event, highlighting the cultural importance of shared joy within family and community.
乐不可支 is considered a somewhat literary or formal idiom (chengyu), but it is widely understood and used in both written and spoken Chinese to add vividness and emphasis.