I once mistyped the word entertainment as entrainment. No wiggly red line appeared underneath, so I realised it was an actual word. One I didn’t know. As I’m just a little odd, I was rather pleased with that … until I looked it up.

It means to get on a train. Why that should disappoint me I can’t really say.
Entrain can also mean to drag along, or when applied to a fluid, to carry particles along in its flow. Eg The tea leaves were entrained from the pot into the cup.Oh! I’ve just cheered myself up by remembering I took a photo (OK lots) of a steam train in Scotland. Three points if you can name it.