Questions & Answers about Я говорю шёпотом в комнате.
Шёпотом is the instrumental case of шёпот (“whisper”).
In Russian, the instrumental case is very often used to express manner — how you do something. A few common patterns:
- говорить шёпотом – to speak in a whisper
- говорить тихим голосом – to speak in a quiet voice
- писать ручкой – to write with a pen
- есть ложкой – to eat with a spoon
So шёпотом here literally means “by whisper” / “with a whisper”, which corresponds in English to “in a whisper” or “in a whispering voice.”
There is an adverb шёпотом in dictionaries as well, but historically and grammatically it comes from the instrumental, and it fits this very typical “instrumental of manner” pattern with говорить.