"In petto" is a Latin phrase that means "within the breast" or "secretly." There are a few synonyms for this phrase, including "in one's heart," "privately," "inwardly," and "concealed." Each of these phrases conveys the idea of something being kept hidden or secret, either within oneself or from others. They can be used in a variety of contexts, from personal emotions and thoughts to business dealings and political maneuverings. Ultimately, these synonyms all suggest a sense of secrecy or privacy, emphasizing the importance of keeping certain things close to one's chest.