The word gruelly is often used to describe something that is harsh, severe, and unkind. There are various synonyms that can be used in place of gruelly depending on the context. Some of the most common synonyms for gruelly include brutal, cruel, merciless, harsh, unforgiving, pitiless, and ruthless. Other options include severe, inclement, unrelenting, tough, and relentless. While each word has a slightly different connotation, all of them can be used to describe a situation or behavior that is unpleasant and difficult to endure. Whether you choose to use gruelly or one of its synonyms, it's important to be precise in your language and select the term that best fits your intended meaning.