“Mum” is one of the commonest words in the language, and it embodies a wide range of meanings — quite apart from its quite separate sense of “silent”, with the word derived from it, “mummery” or “dumb-show”. No, I mean the term we all use to address or refer to a female parent, whether our own or someone else’s.
We all know what Philip Larkin said about our mum and dad. He had to use those two monosyllables for the sake of the rhyme, of course. But he clearly wanted to use the commonest, most familiar words available to him. And I would guess that “Mum” is used by almost everyone now when their own mother is in question. There has been a universal narrowing of vocabulary in this context, almost as though there had been an inexorable external influence compelling us all to abandon our traditionally preferred terms in order to conform to a new egalitarian norm.