knee deep Share definition Flag (sp. also knee-deep) - to stand up to one's knees in sth. - depth ofabout 2-3 feet / half a meter He drowned because he thought the water was just knee deep. He won't make it, he's already knee deep in the quicksand. knee deep by Anonymous November 2, 2003 0 0 Get merch Get the knee deep mug. Buy Now — $32.95 See more merch