Passionlessly indicates the absence of strong emotions or intense feelings. When searching for synonyms, one might consider using words that suggest detachment or indifference, such as apathetically, dispassionately, or coldly. Other possible options include phrases like without conviction or with no zeal. Alternatively, one might use terms that contrast with passion, such as logically, rationally, or coolly. Each of these alternatives can help vary the tone and meaning of a sentence containing the word passionlessly, emphasizing different aspects of the speaker's feelings or attitude. Ultimately, the choice of synonym will depend on the context in which the word is being used and the desired effect on the reader.