Wow! That's certainly a good one. A couple old favorites of mine are: mullet – a hairstyle that is short at the front, long at the back, and ridiculous all around, and regift – to give (an unwanted present) as a gift to another person, in a process which is likely to continue almost indefinitely.

A good éclair is certainly short in duration.

Except that I totally didn't get what "éclair" is.

In which case you're probably looking for an encyclopedia, rather than a dictionary.

The word you are looking for is 'patisserie'.

You'd go to an encyclopedia to find out the history, origins, detailed variations, regional specialities and so on about the topic of éclairs not to understand what an éclair itself is. A dictionary should perfectly well describe a thing without needing to pull out an encyclopedia and if you look at a updated/modern version of the Chambers Dictionary you'll get just such a definition: "A long cake of choux pastry with a cream filling and chocolate or coffee icing."

Anyone know of a good offline version for linux? (besides just searching within an ebook copy)

There is one linked in the article. Stardict format; any reasonable dictionary software will read it.

That appears to be a 2007 copy of Websters? I'm looking for Chambers. Seems that there isn't an ebook of it, just phone apps.

Discovered that their 13th edition accidently left out ~500 words:

https://chambers.co.uk/wp-content/uploads/2016/09/Chambers-M...

Does your modern version have that definition still?

Yes. They removed a lot of the fun definitions in the nineties, but by popular demamd they were brought back!

Funny about the eclair. My girlfriend said the same thing.