'mater' originates from Latin, specifically the word 'mater', where 'mater' meant 'mother'.

'mater' entered English in learned and technical contexts from Latin (via Late Latin/Medieval Latin), appearing in set phrases (e.g., 'alma mater', 'dura mater') and in colloquial slang later on.

Initially it meant 'mother' in Latin; over time the form has been retained in English both for the general sense 'mother' (sometimes slang), and for specialized senses such as anatomical membranes and institutional origins (as in 'alma mater').