I can't think of one off the top of my head.
The word 'brethren' is even more old fashion and formal. (brothers in religious orders)
We wouldn't use the word 'siblings' in conversation when talking about our brothers and sisters but refer to them in a more personal way.
'My brother and two sisters are coming to lunch on Sunday.'
(As an example)
" brother and sister". I looked it up in the dictionary and it says "formal". Is there any other less formal word for it?
I don't know of another collective word for "brothers and sisters", only "siblings". However, I don't think of "siblings" as particularly formal. It's a quicker way of saying "Do you have any brothers and sisters?" - "Do you have any siblings?"
But do look it up in the dictionary! It says "forma". I have never got to hear that one in casual speech.
But do look it up in the dictionary! It says "forma". I have never got to hear that one in casual speech.
I'm not disputing what it says in the dictionary! However, I'm simply saying that in my experience of everyday English, it wouldn't leap out of a sentence at me as particularly formal.
Personally, I wouldn't be surprised to hear someone say in normal, informal conversation "Do you have any siblings?" It is, perhaps, less informal than "brothers and sisters", but in my mind, that doesn't necessarily make it formal!