As nouns the difference between roux and souce
is that roux is a mixture of fat (usually butter) and flour used to thicken sauces and stews while souce is obsolete form of lang=en.
As a verb souce is
obsolete form of lang=en.
roux
English
Noun
(-)
A mixture of fat (usually butter) and flour used to thicken sauces and stews.