What is the antonym of word ridge?

The antonym of "ridge" depends on the context. Here are some possibilities:

For a geographical feature:

* Valley: A low area between hills or mountains.

* Plain: A large area of flat land.

* Depression: A low area in the earth's surface.

For a raised part of something:

* Trough: A long, narrow, hollow, often used to describe the lowest point of a wave.

* Dip: A downward slope or bend.

* Hollow: An empty space within a solid object.

For a line or crest:

* Groove: A long, narrow channel or furrow.

* Crease: A line made by folding something.

* Seam: A line where two pieces of fabric are joined.

To determine the most appropriate antonym, consider the specific context in which "ridge" is used.