No, that’s not something the girls are wearing this year.
If you remember back to some teacher that actually taught you pronunciation, a dipthong* is two consecutive vowels sounds.
I never took Latin, but sometimes in Middle English (and really up to about 1950) there are dipthongs written out in text. I’m reading a book published in 1916, and it uses the dipthong æ in the word hærtico.
The reference is to De Hærtico Comburendo, the law passed in 1401 giving the English King and/or Parliament the right to burn heretics at the stake.
From that, it’s pretty clear that hærtico is equivalent to heretic.
But, I was curious why it would have that spelling with the dipthong. It must mean something, and that is the sound of the “igh” in the word “sigh”.
So, way back when, heretic was pronounced high-retic.
* Dipthong is an obscure enough word these days that my spellchecker flagged it.