Following the thread about children not knowing the word "velvet", and they should know what it means from reading books, let's have some fun with words that used to appear in books a lot, but are less often seen now. Would your own children know them? Some of these, I remember looking up when I came across them. Give your own examples too!
Perambulator
The baths (as in "I'm going to the baths").
Field glasses (The Famous Five)
Bosom (Roald Dahl is fond of it)
Splashery (The only place I've seen this is in the Chalet School books)
Crocodile (not the animal; what children do on school trips)
A PT lesson.