Imagine you are reading 1984 by George Orwell, and you come across this passage:
The voice came from an oblong metal plaque like a dulled mirror which formed part of the surface of the right-hand wall. Winston turned a switch and the voice sank somewhat, though the words were still distinguishable. The instrument (the telescreen, it was called) could be dimmed, but there was no way of shutting it off completely.
So. What shape is the telescreen? Does “oblong” mean “rectangle”?
No, “oblong” means “oval” (AmE)
Statistically, you’re probably American. In that case, it’s possible you’re thinking the telescreen looks like this:
If you are not American, that’s cool too…. To American speakers of English, “oblong” usually means “longer in one direction than the other”, so the adjective describes both rectangles and ovals.
Yes, “oblong” means “rectangle” (BrE)
To speakers of British English, the word “oblong” is an adjective that means “rectangular” or a noun that means “rectangle”.
(So Orwell’s telescreen was not rounded. Oh well.)
What do dictionaries say?
Exactly what I just said, but you don’t have to believe me.
The information at the vocabulary.com page for “oblong” fits my intuition, and includes lots of published examples showing “oblong” used to describe rounded objects.
Dictionaries that contrast AmE and BrE:
The Online Etymology Dictionary page for “oblong” says the word “oblong” has been used as a noun since 1600.
I have difficulty accepting “oblong” as a noun.
I just. I can’t. No. It’s an adjective!
And it strongly connotes “oval-shaped”.