Really and truly are two synonyms that are commonly used in colloquial English to emphasize the truthfulness of a statement. However, there are many other synonyms that can convey the same meaning, such as genuinely, authentically, honestly, veritably, undoubtedly, unmistakably, sincerely, and wholeheartedly. Each of these synonyms has a slightly different connotation, but all of them emphasize the honest and truthful nature of a statement. Whether you are trying to express your sincere feelings, or convince someone of the reality of a situation, using these synonyms can help to reinforce the truthfulness of your words.