unbirthday

Etymology
From, coined by English writer (1832–1898) in  (1871).

Noun

 * 1) A day that is not one's birthday but is celebrated as though it were.

Translations

 * Catalan: no aniversari
 * Dutch: onverjaardag
 * French:
 * German: Nichtgeburtstag
 * Italian: non compleanno
 * Portuguese: desaniversário
 * Russian: день нерожде́ния
 * Spanish: no cumpleaños