Word: Jekyll and Hyde
Definition: The term "Jekyll and Hyde" refers to a person who has two very different sides to their personality. One side is usually kind, good, or gentle (like Dr. Jekyll), and the other side is cruel, evil, or aggressive (like Mr. Hyde). This expression comes from a famous story called "Strange Case of Dr Jekyll and Mr Hyde" by Robert Louis Stevenson, where a scientist creates a potion that turns him into a nasty character.
"Jekyll and Hyde" is a useful term to describe someone with contrasting behaviors or personalities.