trefoil n. + Add to list UK //tɹˈɛfɔɪl// tre·foil SynonymsEtymology Synonyms clovermedicmedickOriginLATtrifolium→OFRtrifoil→MEtrefoil→ENtrefoil From Middle English trefoil, from Old French trifoil, trefeul, from Latin trifolium, from tri- (“three”) + folium (“leaf”).