Synonym is not a synonym of antonym, but antonym is an antonym of synonym.

synonym is words that have same meaning, such as "peak" and "top", so you can say that the synonym of "peak" is "top" and vice-versa. antonym is the word that has an opposite meaning of a word, such as "top" and "bottom", so you can say that the antonym of "top" is "bottom".

synonym is words that has same meaning or its alternative word while antonym is the opposite meaning

Synomim: The words (two or more) which are have the same meaning. Examples: Beautiful=Pretty; Mood=Temper; Good=Well, etc Antonym: The words (two or more) which are have the opposite meaning. Examples: Hot><Cool; Up><Down; Tall><Short; etc