A unique witch coven name from fiction could be 'The Whispering Wind Coven'. It gives the impression of a coven that is in tune with the elements, specifically the wind, and perhaps they communicate in a soft, almost unheard way, like a whisper. Another is 'The Dreamweaver Coven'. This name implies that the coven has the power to manipulate dreams, either to gain knowledge or to influence others in the dream realm.
In fiction, there's 'The Phantom Coven'. This name gives off an air of mystery and intangibility, as phantoms are often associated with the unseen and the unknown. 'The Sunburst Coven' is a unique name too. It could imply a coven that is associated with the power of the sun, perhaps using solar energy in their magic. Also, 'The Mermaid's Kiss Coven' is a really unique name, suggesting a coven that has some connection to the sea or mermaids in their magic practice.