Pane = bread - panino is the diminutive form of pane = little bread and that's what it looks like.
Panino = (bread) roll, panino
If you go to an Italian 'bar' and order a sandwich you get a sandwich, if you order a panino, you get a roll. My answer 'bread roll' was not accepted. I reported it.
And this is what Merriam Webster says: "Definition of panini plural panini or paninis : a usually grilled sandwich made with Italian bread NOTE: Panini is a plural form in Italian but is commonly used as both a singular and a plural in English. Its use as a singular has given rise the variant plural form paninis. The use of panino as a singular form in English has become relatively uncommon as panini has become established as the usual singular."