The word "knarl" is not very commonly used in everyday language. It means a knot or a gnarled growth in wood or a rough or rugged surface. There are a few synonyms that can be used instead of knarl such as knot, burl, gnarl, twist, tangle, crook, contortion, deformity, and irregularity. These words can be used interchangeably to refer to a physical irregularity, a defect or a deformity. In the context of wood, anything that is not smooth or straight can be referred to by one of these synonyms as the opposite of knarl. These words are particularly useful in the fields of woodworking or botany where they describe irregularities on a surface or a tree.