The expression "under a charm" refers to being captivated or enchanted by someone or something. There are various synonyms to describe this state of being, including "spellbound," "mesmerized," "enraptured," "enthralled," "hypnotized," and "beguiled." These words all convey a sense of being under the influence of a powerful force that keeps one captivated and unable to break free. Each word, however, has its own nuances and connotations. For example, "mesmerized" suggests a trance-like state, while "enraptured" implies being carried away by strong emotions. Using a diverse range of synonyms can help to add variety and depth to our writing, while also conveying a precise and nuanced meaning.