There are several synonyms for the word "demonlike" that can convey similar meanings. Some of the common synonyms for demonlike are demonic, devilish, fiendish, infernal, and hellish. These words can be used to describe a person or thing that is evil, frightening, or dangerous. Demonlike could also be replaced with spooky, eerie, or creepy, which can convey an atmosphere or environment that evokes a sense of fear or discomfort. Other options include wicked, malevolent, sinister, and eerie, which can be used to describe a person who embodies or exhibits demonic behavior. Ultimately, the precise choice of synonym would depend on the context and the desired effect.