Some think it was the initials of three men who were involved at the start of the movement that became "HAM" radio. They were HYRUM, ALMAY, and MAXIM.
Urban legend. There's no record of the first two names ever being involved.
Still others think it may have originated with a popular magazine of the day that frequently had articles on the construction of AMATEUR radio equipment. The name of the magazine was "HOME AMATEUR MECHANIC". .
Nope. Another myth.
Other theories started with very amateurish CW ops being called HAM FISTED, and that term "HAM" just migrated to refer to ANYONE using a RADIO to transmit in the newly formed Amateur Radio Service.....
About 100 years ago, the term "ham" was common slang for someone who did a thing only for fun, and who wasn't very good at it. IOW, more enthusiasm than skill or talent. It is still sometimes applied to actors of a certain type.
It was a put-down.
btw, it is not an acronym and should not be written in all capital letters. It's "ham radio" not "HAM radio".
I Wonder WHY it's called a SERVICE?
Because that's the term FCC uses to distinguish different kinds of radio in the regulations.
Here's one for you: Where did the USB/LSB tradition come from in ham radio? (We use LSB on 160/80/40, but USB on 20 and higher).
It's not because there were early SSB rigs with 9 MHz SSB generators and 5 MHz VFOs. The tradition was in place before they existed.
73 de Jim, N2EY