The word ‘Siren’ refers to a device which is able to make a loud and long sound, it is used to broadcast some sort of warning. But in the TVD Universe, the word Siren will remind you of Sybil who belongs to this unique supernatural species. Sirens consumes humans to stay in youth form forever. They serve Arcadius and the only two known sirens in Vampire Diaries are Sybil and Selene.
The term Hybrid refers to an offspring which is born when two different species of organisms are combined. Simply put, its an organism born from two different species. But for the Vampire Diaries fans, the word ‘Hybrid’ will always conjure the image of ‘Klaus Mikaelson’. The first Original Hybrid in the TVD Universe who is born a werewolf and witch, he acquired witch potential from his mother and werewolf genes from his biological father. Afterwards, he is turned into an Original Vampire. After becoming a vampire, he is cut from practicing magic and his werewolf side has been suppressed due to the curse. In Season 2, Klaus is able to lift up the curse which grants him the werewolf powers and abilities.
The word means a person who has gained insight into the mysteries of the universe which is beyond the normal human knowledge, and is able to directly communicate with something divine. But when the Vampire Diaries fans hear the word ‘Mystic’, it can only make them think of the town of ‘Mystic Falls’, a town which is plagued with Supernatural phenomenon, a place where the land carries magical properties. The Mystic Falls town carries a special significance in the TVD Universe, it is the same place where the Originals were born, it is where Katherine & Salvatore love triangle started. Residents of Mystic Falls fight some sort of SPN threat every day.
So when normal people hear the word ‘Cure’, it can make them think of some sort of medicine or medical procedure which could help in recovery from an illness. TVD fans also think in the similar way except being a vampire isn’t the illness, taking the cure could transform a vampire back into human again. Season 4 of the Vampire Diaries majorly revolved around the cure storyline, everyone was desperately seeking in it. In the end, Stefan, Damon, and Elena all transformed back into the humans after taking the cure.