Burnt means cooked too long, until black and bitter. Burnt toast, burnt on the bottom, a burnt smell.
Burnt and burned are both correct past forms of burn; British English prefers burnt as an adjective — burnt toast — and either as a verb. American English prefers burned throughout. Burnt out means exhausted or destroyed by fire, and burnout is the state of exhaustion from overwork. Note burnt offering, both the religious term and the joke about a bad dinner, and burnt sienna and burnt umber, which are paint colours.
1adjectiveburntCooked too long, until black and bitter.
“The bottom of the cake was burnt and the middle was raw.”
Patternburnt + noun (toast, pan, taste) · badly burnt · a burnt smell · burn / burnt / burning
2adjectivedestroyedDestroyed or damaged by fire.
“The burnt shell of the barn is still standing.”
Too few real examples of this word to estimate which sense is commonest.
burnt is a state after fire.
BURNt → it BURNed
It is burn with a t: the toast was burnt, black on both sides, and the whole kitchen smells of it.
hooks ontoburn
Old English brinnan and baernan both existed, one meaning to be on fire and the other to set alight. Middle English merged them into burn, and the two past forms burnt and burned are a small surviving trace of the two original verbs.
Middle English
brent
English, today
burnt
Middle English brent, brynt; by surface analysis, burn + t.
Etymology from Wiktionary, CC BY-SA