dead, died and death

Dead is an adjective.

• a dead man
• Mrs McGinty is dead.
• That idea has been dead for years.

Died is the past tense and past participle of the verb die.

• Shakespeare died in 1616. (not Shakespeare dead …)
• She died in a car crash. (not She is dead in …)
• So far 50 people have died in the fighting.

Note the spelling of the present participle dying (see here).

Death is a noun meaning ‘the end of life’.

• After his death his wife went to live in Canada.

note

For expressions like the dead (= dead people), (see here).