Fade Into Obscurity
When a word or idea that was once big and important suddenly vanishes, like it got hit by a bus and never came back. People forget it, it doesn’t show up in anything, and it’s just left to rot in the corner of the dictionary.
‘What does that word even mean? I’ve never heard of it.’
‘That phrase was everywhere last year. Now it’s just a ghost.’
‘Why is that word not in my vocabulary? It’s like it got deleted.’