立宪 (lì xiàn) literally means 'to establish a constitution' — the character 立 (lì) means 'to set up, to establish', and 宪 (xiàn) is short for 宪法 (xiànfǎ), meaning 'constitution'. Together, 立宪 refers specifically to the formal process of drafting, adopting, and enacting a national constitution, often marking a pivotal moment in a country’s political development — such as transitioning from monarchy to constitutional government. It is a formal, historical, and institutional term, not used for casual or personal contexts.

This word appears frequently in academic, legal, and historical discourse about governance reforms. While it can function as a verb ('to enact a constitution'), it may also appear as a noun in compound terms like 立宪君主制 (lìxiàn jūnzhǔ zhì, 'constitutional monarchy') or 立宪运动 (lìxiàn yùndòng, 'constitutional movement'). It carries strong connotations of modernization, rule of law, and institutional legitimacy — especially in East Asian political history, including late-Qing China and Meiji Japan.