"恒定" (hénɡ dìnɡ) is an adjective meaning "stable" or "unchanging"—emphasizing consistency over time without fluctuation. The first character 恒 (hénɡ) means "eternal" or "constant," conveying enduring quality, while 定 (dìnɡ) means "fixed," "settled," or "determined." Together, they form a compound that stresses unwavering steadiness, often in measurable, scientific, or physiological contexts—such as body temperature, blood pressure, or system performance.

This word is commonly used in formal, technical, or academic settings rather than casual speech. It frequently appears in medical reports, engineering specifications, and physics descriptions where precision and reliability are essential. Unlike more colloquial terms like 稳定 (wěn dìnɡ), 恒定 implies near-perfect constancy—suggesting minimal or zero deviation under varying conditions. Learners should note it’s rarely used for abstract concepts like emotions or relationships; its strength lies in objective, quantifiable stability.