Scylla

In ancient Greek and Roman myth, Scylla was a rock off the Italian coast, personified as an evil monster on the other side of a strait from Charybdis, a whirlpool. If you sailed away to escape either monster, you were in danger of the other one.
English word: The metaphor of Scylla and Charybdis means being caught between two evils -- "between a rock and a hard place."

Selene

Selene was an ancient Greek goddess of the moon, (Roman Luna) even more ancient than the Olympian gods. Over time, she merged with Artemis, to become one of her aspects.

English word: From Selene are derived selenium, a nonmetallic element, and selenology, the science of the moon.

Sibyl

To the ancient Greeks and Romans, a sibyl was a woman who lived in a cave and uttered prophecies. Ten Sibyls were known by the places where they lived. For example, the Sibyl of Cumae lived in a cavern near Naples. My brother and his wife gave me a drawing of this cavern from when they lived near there.

English word: We still use the word sibyl to refer to a prophetess, and the adjective sibylline means "oracular."

Silvanus

Silvanus was the ancient Roman god of the forest. He was akin to Pan, and was often depicted with the lower half of a goat, and the upper half of a man.

Modern Word: From this ancient god we get the words sylvan, "related to a forest," and the names Pennsylvania and Transylvania.

Siren

To the ancient Greeks and Romans, sirens were a group of minor female divinities that sang an irresistible song that enchanted sailors to their doom, as described in the Odyssey. Odysseus had his men put wax in their ears, so they wouldn't hear the sirens singing, while he had the men tie him to the mast of the ship, so he couldn't be lured by the singing, but could still hear it. In form, sirens had the heads, and sometimes the busts and arms, of women, but otherwise had the form of birds.

Modern word: Our word siren retains the original meaning of a dangerous and enticing woman. It also means a device for sounding signals of warning. In addition, it refers to a genus of eel-shaped amphibians.

Somnus

To the ancient Romans, Somnus was the god of sleep (Hypnos to the Greeks). He was said to live in a dark cave where the sun never shone. At the mouth of the cave grew poppies and other plants associated with sleep. Somnus was the father of dreams.

English word: From Somnus, we get somnolent, sleepy, and somnambulism, sleepwalking.

Sors

Sors was the ancient Roman god of luck.

English word: From Sors we get sort, meaning a rank or condition, a kind of any type. We also get sorcery and sorcerer for magic and magic worker.