An acrostic is a message, yes, or at least an intelligible piece of information, and as you described, that word is the primary piece of information that you already have, before you start trying to create an acrostic. HOMES, STEM, and ABBA are not messages or information. They’re just acronyms. In the not-very-good acrostic that I wrote, there’s an intelligible piece of information conveyed by the acrostic word, one that can’t be deduced from the meaning of the rest of the words. ABBA is just an abbreviation of four people’s names. HOMES happens to be a word, but isn’t being used as a word - it’s not referring to anyone’s homes, just acting as a convenient and memorable collection of letters.
If you capriciously redefine “Acrostic” so that its definition just says “see Acronym”, then of course you’re going to find some similarities.
Example: if ABBA was acrostic-like, then they would have started with the familiar word “Abba” that everyone already knew before the band was formed(??), and then worked hard to come up with four lines of clever text that started with those letters.
The student went on to win physics prizes and the teacher was already very renowned, but to give the paper some “class” the teacher asked his friend and future Nobel Prize winner Hans Bethe to co-author this famous Alpher–Bethe–Gamow paper, or αβγ paper.
Fine, great, I’m not going to nitpick definitions with you. Call them Acronyms That Aren’t Abbreviations (ATAA) if it makes you feel better. (ETA: this was addressed to DavidwithanR)
