Alexei mentions in his letters a game called Nain Jaune:
Alexei to Alexandra-November 8, 1916-Mogilev
My Darling, Own, Sweat Dear Mama,
It's warm. Tomorrow I will get up. My salary! I beg you!!!! There's nothing to eatttt! I am also unlucky at nain jaune. So what!!! I shall soon start selling my clothes books and will finally die of hunger. We all kiss your hand!!!! I kiss you many times. Greetings from Joy and Kotka, Toad and Zubrovka. May God keep you!
Alexei to Alexandra-May 18, 1916-Mogilev
Dear Mama,
Yesterday I missed you alot. Together with Papa we sniffed the pillow and the curtain, you know why. Yesterday V. Nicholaevich won alot of money at nain jaune. Today Gilliard had a hair wash. He is as fluffy as a sheep. This ink is impossible. In the evening I prayed for you (+ many times). It feels empty without you. May God protect you.
Your Alexei
I know it's a card game that involved gambling. Does anyone know more on this game?