'ultramafic' originates from the prefix 'ultra-' (from Latin 'ultra', meaning 'beyond') plus the petrological term 'mafic'; 'ultra-' meant 'beyond' and 'mafic' was coined in English from 'magnesium' + 'ferric'.

'mafic' was coined in the early 20th century as a blend of 'magnesium' and 'ferric'; later the prefix 'ultra-' was added to form 'ultramafic', giving the sense 'beyond mafic' and establishing the modern technical term in geology.

Initially it literally meant 'beyond mafic' (i.e., more mafic than mafic); over time it became the standard technical label for rocks extremely low in silica and rich in Mg and Fe.