Quotation к Кохелет 1:17

The word that means foolishness, sikhlut, could also mean cleverness, from sekhel. The fundamental importance of this double meaning is not lost on Kohelet.

The Hebrew here is ra'ion ruakh, closely related to ra'ut ruakh (befriending the wind). Ra'ion means idea or notion, so the phrase could mean "notion of spirit", or "idea of wind". The concept is that perception has a quality of floating somewhat freely, even wandering, from the determined reality of the physical world.