n. The anniversary of that night in subsequent years.
the GNU version of the Collaborative International Dictionary of English
n. The night in which a person is born; the anniversary of that night in succeeding years.
The Century Dictionary and Cyclopedia
n. The night of the day on which a person is born; the anniversary of that night.
Word Usage
"One night in May — it was her birthnight, and twenty years since she had left her home — Hugh Graham sat in the room she had hallowed in his boyish days."