The word "agelastic" means the absence or loss of laughter or the ability to laugh. There are a few synonyms for this word including gloomy, cheerless, unamused, and sober. Other words that could be used interchangeably with "agelastic" include grim, serious, depressed, and humorless. While all of these words convey a sense of negativity or lack of humor, they are different in specific connotations. For example, "cheerless" specifically means lacking cheer or happiness, while "unamused" indicates a lack of amusement or entertainment. Nonetheless, all of these synonyms can be used effectively to describe someone who is agelastic.