Names for 'the other granny'.

I've been enjoying the thread about grandfathers' names, and this has prompted me to ask if any of you refers to his or her opposite number using a particular word. If I mention my son's mother-in-law in conversation, for instance, it would be great to be able to use a specific name, but it doesn't seem to be usual. There is a Hebrew word, but I'm not sure enough of what it is to risk writing it here. If you know it, please remind me. But how many people would understand it? I used to live in NW London, but here in the Scottish Borders I have come across very few Hebrew or Yiddish speakers, in fact none. So how do you refer to these members of your extended family?