the.com/mater

means An old-fashioned, upper-crust British term for one's mother, used mostly in a jokey or affectionate way now.

from Simply the Latin word for 'mother' (as in 'maternal'), lifted straight into English. It stuck around in Britain partly through Latin-heavy schooling in public schools, where boys referred to 'the mater' and 'the pater' (father) with a mix of formality and schoolboy irony — a habit that outlived the Latin lessons and became a marker of posh, slightly theatrical Englishness.