速度 (sù dù) is a noun meaning 'speed' — the rate at which something moves or happens. It combines 速 (sù), meaning 'fast' or 'swift', and 度 (dù), meaning 'degree' or 'measure', literally forming 'measure of swiftness'. Unlike English, where 'speed' can sometimes be used as a verb ('speed up'), 速度 is strictly a noun in Chinese and must be paired with verbs like 提高 (tígāo, 'increase') or 降低 (jiàngdī, 'decrease') to express change.

This word appears frequently in contexts involving motion, technology, performance, and biology — for example, describing how fast an animal runs, how quickly data transfers, or how rapidly a process unfolds. It’s neutral in register and used in both spoken and written Mandarin, though in casual speech, people may shorten it to 速 (sù) in compound terms like 加速 (jiāsù, 'accelerate').