Unpassionate is a word that means lacking in enthusiasm or passion. There are several other synonyms that can be used instead of unpassionate, such as apathetic, indifferent, dispassionate, unemotional, unenthused, unexcited, uninterested, unenthusiastic, and emotionless. These synonyms can be used to describe a person who has a flat affect or who is not engaged in a conversation or activity. They can also be used to describe a situation or object that is devoid of any excitement or interest. Using synonyms can make your writing more interesting and varied, so it's always a good idea to keep a thesaurus handy.