I recently came across the idiom "Be mother" in a crossword. It is supposed to mean 'to pour tea'. I was surprised by the meaning, and want to ask if there is any etymology or history behind this curious idiom. Is it informal/facetious/slang?
It's normally heard as Shall I be mother? meaning 'Shall I pour the tea?' It's used because pouring the tea has traditionally been seen as a mother's role. I suspect it's now heard less than it once was for various social rather than linguistic reasons. It's not slang and it's not facetious, but because of the nature of tea-drinking it's likely to be heard in informal situations.
It is also a saying that stems from the superstition that a female guest should never pour the tea in another woman's household - for then she would fall pregnant.
So should a woman offer to pour the tea in another woman's household ("I'll be mother"), she desires to become a mother. Or it may also be used as tongue-in-cheek by those who are not in the least superstitious.
From author and folk historian Dr. Alec Gill:
Tea-drinking and fertility were intermingled. Indeed, the tea-pouring clich‚ "I'll be Mother" stems directly from primitive superstition. The consequences of two people pouring from the same pot could be dire.
During the 1930s, if a man and woman took turns in pouring, a child would be born to them. A female visitor must not pour tea in another woman's house - otherwise, she would fall pregnant. This evolved to having twins and - even worse at the superstitious level - ginger-headed twins.
Thus, an early form of birth-control was to let only one person do all the pouring in company!
Traditionally the mother in a family pours the tea. So "being mother" means "pouring tea".
It's as simple as that.
I don't think the phrase "be mother" specifically means to pour tea. It's used, in my experience, when one adult is serving something to another adult and that person could easily serve themselves. Because a child isn't usually allowed to serve him or herself at the table, their mother does it for them. So if someone is serving something to another person, they are "being mother".
It's not just about tea.