Answer:
False
Step-by-step explanation:
You can use synonyms in your speech, but the wording of this phrase doesn't sound correct at all. That because for it to be true, you'd have to use a very broad definition of what is part of a speech such as "a word is a part of speech". Also, the use of the articule indicates that a single synonym would be part of speech, which also sounds very weird. Synonyms, in fact, are: "words or phrases that mean exactly or nearly the same as another word or phrase in the same language, for example shut is a synonym of close."