Vociferant is a term used to describe someone who is loud and vehement in their opinions or speech. Antonyms for this word would be someone who is quiet, reserved, or restrained in their manner of speaking. Some synonyms that could be considered antonyms include words like soft-spoken, whispered, or mumbled. Other possible antonyms could include words like docile, meek, or timid, which describe someone who is not inclined to speak up or make a fuss. Ultimately, the choice of antonym for vociferant will depend on the context in which the word is being used and the specific nuances of meaning that the writer or speaker wishes to convey.