A knot in a tree is a type of growth that forms when a branch or root grows around itself, creating a hard, woody lump. The term 'knot in a tree' can be broken down into three crossword solutions: GNARL (5 letters), KNAR (4 letters), and BURL (4 letters). GNARL is an adjective meaning twisted or gnarled, while KNAR is a verb meaning to twist or curl, and BURL is a noun referring to a rounded outgrowth on a tree trunk or branch.