Hi Folks,
As Fernando says, though I’ll add the following:
The etymology of the word “facon” derives from the Portuguese and old Castillian word “faca”, meaning knife. So “facon” means large knife, any large knife and this is how the term is still used in popular parlance.
However, modern writers on the subject and curators have narrowed the scope of the term to knives that meet the description given by Fernando, so as to be able to establish various other typologies based on their descriptive attributes.
In the course of the 19th century the term “gaucho” gradually changed from an appellation describing mounted vagabonds to include any agricultural worker and these folks were only allowed knives that were fit for hacienda/ranch work and thus facons were effectively outlawed; And in this context a “facon” was any large knife ill suited for work and conducive to violence.
For those interested, there is a rather good article on this subject in Spanish in Wikipedia, much better than the one in English, and which is worth translating:
https://es.wikipedia.org/wiki/Fac%C3%B3n
Cheers
Chris