What is a antonym for biped?

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.

quetion(s)

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".

Some words do not have direct opposites [antonyms]. The word "but" has no antonym. (head)

coal