Formal:
* Synonyms: This is the most common and straightforward term.
* Equivalents: Emphasizes the words' complete interchangeability in meaning.
* Near synonyms: Used when the words have similar but not identical meanings, perhaps with subtle nuances.
* Lexical variants: This term focuses on the words' different forms but shared meaning, often used in linguistic analysis.
Informal:
* Mean the same thing: This is a simple and direct way to describe the relationship.
* Say the same thing: Similar to "mean the same thing" but emphasizes the words' function in communication.
* Are interchangeable: Focuses on the ability to use one word for the other in any context.
Examples:
* "Happy" and "joyful" are synonyms.
* "Big" and "large" are equivalents.
* "Brave" and "courageous" are near synonyms, with "courageous" suggesting a stronger sense of bravery.
* "Automobile" and "car" are lexical variants.
* "Good" and "nice" mean the same thing.
* "Start" and "begin" say the same thing.
* "Quickly" and "rapidly" are interchangeable.
The best way to describe two words that have the same meaning depends on your audience and the specific situation.