foil
definition
a character or object that contrasts with another to highlight particular qualities
example
In the story, the brave hero has a foil who is a cowardly character, which makes his bravery stand out.
synonyms
counterpartcontrastopposite
word origin — From Middle English 'foilen', meaning 'to cover or plate,' originally referring to a type of thin metal used in fencing, later adapted to describe a contrasting character.