We have had several threads on how a particular word gets into a dictionary, but now I'm wondering the opposite. I am re-reading a Mary Stewart novel, vintage 1967, in which the main character and her companion come across a Chambers Dictionary, from which the main character reads the word cusk, and asks whether her companion knew that a cusk is a torsk or a burbot. Well, MY newish Chambers being to hand (hi, Jo!), I found that it contained torsk and burbot but not cusk. So--how is it decided that a word should be dropped from a dictionary?