Synonyms : Synonyms Words with the same or similar meaning
fat and chubby, mad and angry,
happy and glad, hungry and famished
Antonyms : Antonyms Words with opposite meanings
Sad and happy, silly and serious, pretty and ugly, smart and stupid.
Why the heck do we need to know these terms? : Why the heck do we need to know these terms? It makes your writing a lot more interesting if you mix up your word choice.
You can better describe your thoughts and feelings on different subjects.