When someone says something "in jest", they are not being serious. There are several synonyms for "in jest" such as jokingly, teasingly, playfully, whimsically, light-heartedly, amusingly, humorously, tongue-in-cheek, facetiously. These words convey the same lighthearted tone as "in jest" and can be used interchangeably in a sentence. For example, instead of saying "I didn't mean it", one can say "I was just jokingly teasing you". Using synonyms for "in jest" can add variety and depth to one's language, making their dialogue sound more interesting and engaging.