@kate@Sylvhem The word ‘nibling’ was right there, Auntie Anne! 😉
Admittedly, I only just discovered that it existed back then!
It was apparently coined in 1951 – maybe – by linguist Samuel E Martin, and the Merriam-Webster post which contains this information does concede that it took half a century to gain any sort of traction: https://www.merriam-webster.com/wordplay/words-were-watching-nibling
The OED, where I looked first, doesn’t even acknowledge the word’s existence, let alone offer any insight into its history – poor show!