Where did the term "mono block" originate?

I don't know but I'd guess it is because the mono-amps, being simple 1 channel amps with one input and one output, were generally a simple hexahedron, resembling a block.

Maybe the person who coined the phrase was fond of these guys,

All the best,
Nonoise

If u think of it I’m sure it would come to u. 🤷‍♂️

Not sure of the origin, but the term itself is my 2nd favorite part of having mono blocks. 😎

Why isn't or when is a stereo amplifier a "stereo block"?

The word comes from outside of audio, and probably comes from manufacturing. 

Originally all amplifiers were "mono blocks" but they weren't called that.  THey were just amplifiers.  At this time stereo was not real and 1 amplifier was all you needed. :)  See if you can find some vintage tube amps made for the early motion picture theaters. 

Then stereo came out (1930s per https://en.wikipedia.org/wiki/Stereophonic_sound#History)  and they were just "stereos" and stereo amplifiers became the normal way of packaging an amplifier. 

So the term monoblock applied to an amplifier probably came at some time after that.

                                          Semantic Gymnastics!

     Perhaps: because some think of various system topologies*, as being built of individual, "blocks" (syn: pieces, parts, components) and the long version is, "monoblock amplifier", as opposed to, "stereophonic amplifier."

  "Not sure of the origin, but the term itself is my 2nd favorite part of having mono blocks."

                                                     Me too!

       Suppose LEGOs had preceded blocks, as the World's favorite building unit: mono-LEGO amplifiers?    

                               Just doesn't have the same ring to it!

*: https://www.ooberpad.com/blogs/audio-video-tips/what-is-the-difference-between-a-regular-amplifier-and-a-monoblock#:~:text=A%20monoblock%20amplifier%20is%20a,share%20a%20common%20power%20supply.

I got a pair of Krell KMA 100s back in the early 80s and back then they were just mono amps. The block came after. I cannot say where it originated. They were more squarish than stereo amps and instead of putting them in cabinets we stuck them on the floor either behind or between the loudspeakers. They looked like blocks so the term is not a stretch. I now have mono amps that are under the speakers and are in no way shape or form blockish. They look more like a whore house chandelier:-)

Dang… that’s a nice whorehouse!

From ChatGPT:

The term "mono" comes from the Greek word "monos," meaning "single" or "one." In audio terminology, "mono" is used to describe a single audio channel, as opposed to stereo, which involves two separate channels for left and right audio.

The word "block" in this context refers to a self-contained unit or component. In the case of monoblock amplifiers, they are often designed as compact, single-channel units that can be easily installed or integrated into audio systems.

So, when these two terms are combined, "monoblock" essentially means a self-contained amplifier unit dedicated to powering a single audio channel, typically used in mono audio setups or in multi-channel systems where individual amplifiers are used for each channel to achieve higher power output or more precise control over speaker performance.

Regards,

barts

Fun question @williambf 

and I’ll be curious to hear the definitive answer.

The term mono blocks was probably picked up along the way as someone referred to them as that and it just caught on. Such is language.

All the best,
Nonoise