The seeds of the plant Nigella sativa used as a spice.
love-in-a-mist
noun
Nigella damascena, an annual flowering plant of the genus Nigella, the blooms of which are generally blue in colour, though also found in shades of pink, white or pale purple.
How often have the words kalonji and love-in-a-mist occurred in a corpus of books? (source: Google Ngram Viewer )