On May 23, 7:52 am, Bertie the Bunyip wrote:
wrote i
So it's a process to cause the air to exert a force in a
direction perpendicular to the airflow. It fools the air, if you like,
which is why we call it an "air foil." A foil is a device to deceive.


Actually it's a synonym for blade.


Not quite. From the Merriam-Webster Dictionary:

Foil:
1 obsolete : trample
2 a: to prevent from attaining an end : defeat always able to foil
her enemies b: to bring to naught : thwart (foiled the plot)
synonyms: see frustrate.

So my "deceive" is much less accurate than "frustrate."

Your definiton matches one of the the Cambridge Dictionary's
definitions:

foil (SWORD) gatiful
noun [C]
a thin light sword used in the sport of fencing


Dan