The root “Sha” comes from the way shepherds manage their flock.
To guide their animals, shepherds call out the exclamation saa…ssa… with sounds like za, ss, or z…

Saóō and all meanings of sa-óō are directly related to the safety of the flock. A related example is the sound xiu-xiu, used to scare away birds.
It is also connected to saving from death, preserving life, safeguarding, keeping something secure, and remembering. Shepherds had to remember all their animals very well, so that at night, when they gathered them into the pen, they could notice without counting or error if one was missing.
From all these meanings come other words like sóos (safe), sostós (correct), sōsívion (life preserver), sōmós (whole), sōtḗr (savior), and Sōkrátēs (Socrates).

Seiō, to shake, comes from the verb saoō, which becomes saō and then sa combined with hēmi, to set in motion, meaning to initiate movement. Together with the root i, it becomes sa-i-ō, which then turns into saíō, a form similar to seíō, expressing animalistic or lively motion.
It is used in reference to a person who dances, or shakes, who disturbs or makes noises, or even when falsely accuses, as well as when a person suffers an earthquake. From it derive words like diásēsis (concussion), seisachtheia (relief from burden), seisíchthōn (earth-shaker), and seístro (sistrum).

Sitos (wheat) is derived from seíō (to shake), when ei becomes i, since during winnowing wheat is constantly shaken, like ears of grain in the wind.
From this root come the words sitári, which is wheat, krithári aka barley, chórto which is grass or herb, ártos is bread, trofí which is food, as well as síteusis meaning fattening/feed, and the verbs siteúō, to feed/fatten, and parasiteúō, to parasite and live off others.

Nēsteúō, to fast, on the other hand, comes from the negation nē- and siteúō, meaning abstention from food, hence the word nēsteía, fasting.

Erini, traditional song of Tilos
Erini where were you at the daybreak
where were, where were, where were you at noon
where were you at the sunset
Orange, orange, orange-scented
Mother, we didn’t have water
mother thirst I had, mother thirst I had
And I grab the silver jug
the apple, the apple, the apple in my hand
And I go to the holy spring
to drink and drink and drink and fill it up
And then where I fill up
and when, and when, and when I wanted to leave
I find the lad and he lies
in the well, in the well and in the well and he sleeps
Get up lad to drink water
to eat and eat and eat a juicy apple
To smell basil
and rise, and rise, and rise your soul
And then they took the water from the stars
the clouds, the clouds, the clouds from the well
They took my little jug too
the night, the night, the night wanderers