What is the synonym of rille?

There isn't a single perfect synonym for "rille," as its meaning depends on the context. Here are some possibilities based on different meanings of "rille":

In geology/astronomy:

* Furrow: This is the most common synonym, particularly when referring to linear depressions on the Moon or other celestial bodies.

* Channel: This can be used for rilles that resemble waterways or drainage channels.

* Gully: This is a synonym when referring to a narrow, steep-sided ravine, although it's often used for features on Earth.

* Trench: This emphasizes the narrowness and depth of the feature, particularly if it's man-made.

In other contexts:

* Groove: This is a synonym for a linear indentation or depression in a surface, but it's less specific than "rille."

* Line: This is a very general synonym, particularly when referring to a visual representation of a rille.

To choose the best synonym, consider the context and what aspect of the rille you want to emphasize.