Apologies to those who have heard this from me before, but in the North East (England) glass industry the word had very specific meanings. Both Sowerbys and Davidsons used "flint" to mean colourless soda lime glass. Whether or not it was later acid etched was irrelevant. Joblings used the term in their "Flint Factory", which was how they described their traditional pressed glass department. The word "flint" was therefore used in Sunderland, locally and rather loosely, to describe anything, regardless of colour, which wasn't "Pyrex"!!
Of course, in the optical and cut glass industries we have different meanings again. My best advice would be to stay well away from the word!