Piscine means relating to fish. A piscine creature lives in water and has fins, scales, and gills. When scientists study piscine behavior, they're investigating how fish swim, hunt, hide from predators, or interact with each other.

You might encounter it in books about marine biology or nature writing. An author describing a river ecosystem might note the piscine inhabitants darting between rocks, or a nature documentary might discuss the piscine diversity of a coral reef, meaning all the different types of fish living there.

Sometimes people use piscine to describe something that reminds them of fish, even if it isn't actually a fish. A swimmer doing the butterfly stroke with smooth, wave-like movements might be described as moving in a piscine way. An architect might design a building with curved, flowing lines inspired by piscine forms.

The word isn't common in everyday conversation. Most people would just say “fishy” or “fishlike,” but piscine appears often enough in scientific writing and literature that it's worth knowing when you come across it.