The word means a very small quantity of something, and I never saw it before reading Bob Sloan’s mystery, Bliss Jumps the Gun. Since then, I’ve seen it several times. It is a French word and pronounced Soop-sawn because of the little cedilla below the c. It took me damn forever to figure out how to put that into the text box.
I tried to find the value of this word, why someone would use it instead of, let’s say, iota. The O.E.D. had an interesting take. The define soupçon as a suspicion or suggestion of something. How poetic. While an iota may be a small amount, a soupçon is so minuscule that it is not even visible, merely the slight hint of its existence is left.