The history and use of the term mugearite and its relation to the terms trachydolerite, oligoclase andesite, and oligoclase basalt are discussed. It is proposed that (1) the term oligoclase andesite should be abandoned, (2) the term mugearite should denote a fine-grained aphyric or microphyric rock rich in oligoclase with orthoclase, olivine, and iron ore as less abundant major constituents, and with a trachytic appearance, (3) the term oligoclase basalt should denote rocks similar chemically to the mugearites but basaltic in appearance.