Lluath Share definition Flag A Welsh word meaning 'idiot' or thick! Basically someone with very little intelligence that you have no time for.Pronounces THU-ATH There's that bloke Jon that we used to work with. He was thick as pig shit. What a total lluath. Lluath by Rubo Leaf February 10, 2010 0 0 Get merch Get the Lluath mug. Buy Now — $32.95 See more merch