It's what I thought at first too but "2 verres" of it are suggested, which is a little bit too much!I think this must be some kind of eau de vie - of which there are many flavours. I'm guessing you choose according to your liking. If it's for salad, I guess a sprinkling of eau de vie (i.e. fruit-based) would add flavour.
(2.5 cl approx)
But shot glasses are not uniform in size