"The term originated from the Greek atheos was a derogatory term which literally meant without Gods."
The term still literally means "without gods." Some religious people may use the term derogatorily but atheists do not.
Atheists do not necessarily eschew belief in gods. It is enough that they do not hold such beliefs.
All infants are implicit atheists.
To suppose that free thought first appeared in the 18th century is absurd.