"Ignis-fatuus" is a Latin phrase that means "foolish fire." This term has been used to describe the eerie, flickering flames that can be seen over swamps, indicating the presence of natural gases. There are several synonyms for ignis-fatuus that can be used to describe these mysterious flames. These include "will-o'-the-wisp," "jack-o'-lantern," "fairy light," "sprite," "ghost light," and "hinkypunk." These words are commonly used in folklore and literature and have been associated with supernatural beings, such as fairies and ghosts. While the term ignis-fatuus might not be commonly used today, its synonyms continue to be used in popular culture to describe the eerie, mysterious lights that can be seen over swamps and marshes.