Words with the same meaning
I believe the answer is:
synonyms
'words with the same meaning' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for synonyms that I've seen before include "Words that can be interchanged with others" , "Interchangeable words" , "Two words that can be interchanged" , "Words with meanings similar to those of others" , "Two words with the same meaning" .)