The word "devilish" is an adjective that describes something or someone as resembling, characteristic of, or associated with the devil. It can be used to describe behavior or appearance that is mischievous, wicked, cunning, malicious, or evil in nature. For example, one might say that a person's devilish grin indicates they are up to no good, while a situation described as "devilishly complicated" would imply it is difficult and challenging to navigate.