491. Misuse of coward as an adjective
(X) She said, 'You are a coward boy.'
(O) She said, 'You are a coward.'
"Coward" (= one without courage) is a noun. The adjective is "cowardly".
492. Misuse of others as an adjective
(X) The others boys aren't here.
(O) The other boys aren't here.
"Others" isn't an adjective but a pronoun. The adjective is "other" (without the "s").
We can say: The others aren't here, omitting the noun boys.
493. Misuse of died for dead
(X) I think his grandfather is died.
(O) I think his grandfather is dead.
"Died" is the past tense of "die". The adjective is "dead".