flu·el·lin noun alsoflu·el·len\flüˈelə̇n\ (-s) Etymology: Welsh llysiau Llywelyn, literally, Llewelyn's herbs, probably after Llywelyn ab Iorwerth (Llewelyn the Great) died 1240 or Llywelyn ab Gruffydd died 1282 princes of Wales 1.: either of two speedwells (Veronica officinalis and V. chamaedrys) 2.: toadflax 3.: cancerwort 4.: mountain parsley