Italian plural of panino (small bread roll), from Latin panis (bread) — used in English as a singular noun for a pressed grilled sandwich
A pressed and grilled sandwich made with Italian bread, typically ciabatta or focaccia
From Italian 'panini', the plural of 'panino' meaning a small bread roll, diminutive of 'pane' meaning bread, from Latin 'panis' (bread). In Italian, panino refers to a single filled roll; panini is the plural. English borrowed the plural form and uses it as both singular and plural, which irritates Italian speakers. The grilled, pressed preparation that English speakers associate with panini is largely an American and British innovation. Key roots: *pa- (Proto-Indo-European: "to feed, to protect").
The English word companion comes from the same Latin root panis (bread) — a companion is literally someone you share bread with (com- together + panis bread). Company has the same origin. The act of breaking bread together has been embedded in the language of human connection for over two thousand years.