panini (n.)

by 1974, originally in an Italian context, where the word means "small bread rolls," typically filled sandwich style; plural of panino, a diminutive of pane "bread," from Latin panis "bread," from PIE root *pa- "to feed."  Used since c. 1980 on U.S. restaurant menus in reference to sandwiches made with a small flat loaf of Italian bread.

Today they have a well-established niche in any sandwich outlet. In the process of their Anglicization, their plurality has been a problem; increasingly panini is interpreted as singular, and a new plural paninis has been created .... [Ayto, "Diner's Dictionary"]