Antonyms are basically just words with opposite meanings to one another. Conversely, synonyms are words with meanings that are the same as one another. Most people don’t know that there are, in fact, different types of antonyms though.
Two things that are altogether different are opposite: Antonyms are words of opposite meaning."It is said that opposite characters make a union happiest" (Charles Reade).
Of a totally or radically different nature, quality, or tendency; also (of two persons or things), mutually antagonistic or repugnant; mutually opposed in character or action; contradictory; non-congruent: as, words of opposite meaning; opposite terms.
Find 106 different ways to say OPPOSITE, along with antonyms, related words, and example sentences at Thesaurus.com.
There are 15 meanings listed in OED's entry for the word opposite, five of which are labelled obsolete. See ‘Meaning & use’ for definitions, usage, and quotation evidence.