The story
From wolf + star: Remus Lupin is a werewolf; and Sirius Black is named after the dog star Sirius (Sirius Black is an animagus who turns into a dog).
Etymology from Wiktionary, CC BY-SA 4.0.
Wolfstar
Today it means: The ship of characters Remus Lupin and Sirius Black of the Harry Potter series. Full definition →