A rill is a tiny stream of water, smaller than a creek or brook. Picture the smallest trickle of water you can imagine flowing down a hillside after rain, carving a miniature channel through the dirt. That's a rill.

Rills form when rainwater flows downhill and starts to cut little grooves into soil or sand. You might spot them at the beach where water runs down from the dunes, or on a muddy slope after a storm. Each rill is like nature's first draft of a river: given enough time and water, some rills can grow deeper and wider, eventually becoming gullies or even full streams.

The word also appears in poetry and literature to describe any small, musical flow of water. Writers use rill when they want to evoke something delicate and peaceful, like the gentle sound of water trickling over stones. It's a word that sounds like what it describes: soft and flowing.