Middle English Alternative forms nyþeful niðful, niþfull, nyðful (Early Middle English) Etymology Inherited from Old English nīþfull; by surface analysis, nith + -ful. Pronunciation IPA(key): /ˈniːθful/ Adjective nithful (poetic) Hateful, malign, jealous; showing envy or hate. References “nīthful, adj.”, in MED Online, Ann Arbor, Mich.: University of Michigan, 2007. Wikiwand - on Seamless Wikipedia browsing. On steroids.