The phrase "synonyms upon" appears to be incorrect or not a standard English phrase. It’s possible you meant “synonyms of” or “synonyms for.” Synonyms are words that have similar meanings. For example, "happy" and "joyful" are synonyms because they express similar feelings.
The word "synonym" comes from the Greek "synonymon," which is derived from "syn-" meaning "together" and "onym" meaning "name." This indicates a word that shares a similar name or meaning with another.
If the word "synonyms upon" was indeed a typo or an incorrect form, these interpretations and explanations could clarify its intended meaning.