Placate means to 'sooth or pacify' therefore the antonym would be 'agitate, upset or worry' The antonym of 'ferocious' would be 'gentle, innocent, kind, tame or tender
The opposite (antonym) of antonym is synonym. An antonym is a word that means the opposite. A synonym is a word that means the same thing, or nearly the same thing, for a given context.
Some words do not have direct opposites [antonyms]. Antonyms do not usually substitute for phrases. The phrase "you are" has no antonym. A contrasting version of "you are" is "you are not".
