突起 (tū qǐ) is a noun meaning 'a protrusion' or 'a sudden bulge' — a physical feature that sticks out from a surface. The character 突 (tū) conveys suddenness, abruptness, or bursting forth, while 起 (qǐ) means 'to rise' or 'to lift up'; together, they emphasize an upward or outward projection that stands apart from its surroundings. It’s commonly used in anatomical, biological, and geological contexts to describe natural bumps, ridges, or swellings — such as on animal skin, bone structures, or rock formations.

This word carries a neutral, descriptive tone and appears frequently in scientific or technical writing, though it can also appear in everyday descriptions of irregular surfaces. Unlike the verb phrase 突然起来 (to suddenly arise), 突起 functions exclusively as a noun and never as a verb. It’s often modified by adjectives like '明显的' (obvious) or '骨性' (bony), especially in medical or zoological texts.