Here are some examples:
* "Happy" and "joyful" are synonymous.
* "Big" and "large" are synonymous.
* "Expensive" and "costly" are synonymous.
In essence, synonymous words can be used interchangeably without significantly changing the meaning of a sentence.
However, it's important to remember that while synonymous words have similar meanings, they might not be perfect substitutes in all contexts. Sometimes, one word might be more appropriate or have a slightly different nuance than the other.