Of Greek or Slavic origin.
Means moonlight.
Sources mention meaning of the name Sileny to be “silence”, by association with the English word “silence”.
In that case, Sileny is of Latin origin, from the Latin word “silentium”, meaning “be quite”.
Another association of Sileny, is the name Selene, also Selena.
From the ancient Greek Selene.
In Greek mythology Selene is the goddess of the moon, often identified with the goddess Artemis.