“SIHAYA: Fremen: the desert springtime with religious overtones implying the time of fruitfulness and “the paradise to come.” -Terminology of the Imperium
Sihaya, the Fremen term for the desert springtime, is relevant for at least two reasons. First, it was a term of endearment that Paul Atreides used for his love and concubine Chani. Second, the same name is used in the cosmology created by Leto II. In describing the meaning of Siyanoq to Moneo, Leto states that Sihaya is the name of the Recording Angel "who interrogates the newly dead.” It's reasonable to assume that Leto was incorporating his mother as a semi-divine part of his mythology. The incorporation of his family into his personal cosmology is also confirmed by Siona and Nayla's mention of the "Prayer to Ghanima", Leto's beloved sister.