/ˈjīrəs/
Noun, pl. gyri
1. A ridge on the cerebral cortex. It is generally surrounded by one or more sulci (depressions or furrows; sg. sulcus). (wikipedia.org)
2. A ridge or fold on the cerebral cortex. (wiktionary.org)
3. Any of the many sinuous ridges or bumps on the surface of the brain that is surrounded by one or more sulci. (biology-online.org)
4. A ridge or fold between two clefts on the cerebral surface in the brain. (Google Dictionary)
5. A convex fold or elevation in the surface of the brain. (wordnetweb.princeton.edu)
Word origin: From Latin gyrus “circle, circuit, career,” from Greek gyros “ring, circle.”