Gnarl

A knot in wood; a large or hard knot, or a protuberance with twisted grain, on a tree.

Something resembling a knot in wood, such as in stone or limbs.

The average value of the magnitude squared of the curl of a vector field over a continuous path that is tangent to the vector field at every point. In mathematical notation, gnarl is represented by the lowercase Greek letter ξ.

To knot or twist something.

To snarl or growl; to gnar.