> an Opus is longer than a Sonnet

And people know this? I didn't. I am not into music or poetry so these are not terms I am familiar with.

I guess you are one of today's lucky 10,000 [0]

[0] https://xkcd.com/1053/

Not as lucky as the guy seeing the Mentos/Soda trick for the first time!

This inspired me to check lol. Brysbaert et al. (2019) collected word prevalence norms (the share of people who report knowing each word) for ~62K English lemmas from ~220K participants.

fable: 99/100 sonnet: 97/100 haiku: 91/100 opus: 89/100

So while these terms are almost universally known, opus is indeed the least known of the four. And I guess this only measures whether a person knows a word, not whether they know an opus is longer than a sonnet! Personally I only inferred that based on the related term 'magnum opus.'

An opus is just short for "magnum opus", and it's a different type of label than a sonnet. A sonnet is a very particular kind of poem, while "opus" basically just means an important work. It can be short or long, and has no format requirements like sonnet (or haiku does).

And fables are not particularly long actually.

To clarify: opus is not the same thing as έπος (épos), which is rendered as epic in English, both as adjective and noun. An έπος is indeed a type of long written work, but opus (work) is unrelated etymologically, they come from different Proto-Indo-European roots.