This is the 11469th most frequent Turkish word.
estiği
"Estiği" means "when/where it blows" (referring to wind).
In this sentence, 'estiği' refers to the action of the wind blowing, in a dependent clause describing the conditions when leaves sway.
Rüzgar estiği zaman yapraklar sallanır.
When the wind blows, the leaves sway.
In this sentence, 'estiği' is used metaphorically to describe the spontaneity of actions.
Hikayeyi anlatırken estiği gibi davranıyordu.
While telling the story, he was acting as if whatever came to mind.
Here, 'estiği' describes the action of the sea scent spreading through the air.