Biscuit
What it really means
The British word for a cookie — a hard sweet snack often dunked in tea (digestives, hobnobs, rich tea). What Americans call a "biscuit" (soft bread roll) does not really exist here.
Context, tips & common mistakes
A British biscuit is an American cookie — crisp, sweet, sized for tea — and the vocabulary swap matters in both directions: a 'cookie' in Britain specifically means the larger, softer, chocolate-chip style; the American 'biscuits and gravy' breakfast item simply does not exist here. Biscuits live with tea: the dunk (briefly submerging the biscuit) is national practice with its own physics, since every variety has a known structural failure time.
The canon runs digestive (plain or chocolate), rich tea (austere, superb dunker), hobnob (oaty, robust), custard cream and bourbon (sandwich biscuits), Jaffa cake (legally a cake, culturally a biscuit, famously litigated). The office biscuit tin is a social institution — contributing packets earns quiet credit, and offering the last biscuit rather than taking it is textbook workplace diplomacy.