To cut one or more grooves in (the ground, etc.).
To wrinkle.
To pull one's brows or eyebrows together due to concentration, worry, etc.
A trench cut in the soil, as when plowed in order to plant a crop.
Any trench, channel, or groove, as in wood or metal.
A deep wrinkle in the skin of the face, especially on the forehead.
To undo a folding.
To release from a fold or pen.
To turn out; to happen; to develop.
To open (anything covered or closed); to lay open to view or contemplation; to bring out in all the details, or by successive development.
To reveal.
In functional programming, a kind of higher-order function that is the opposite of a fold.