tartare a French word which has been in use since the 13th century and refers to the Tatars (the name of one of the tribes of the Turco-Mongol peoples of C. Asia who were renowned for their fierceness). The term’s meanings in the kitchen involve piquancy.
Sauce tartare is a mayonnaise made with hard-boiled egg yolk and the addition of onion/spring onion/chives; or finely chopped gherkins, capers, and fines herbes. It is served with fish, pig’s trotters, etc.
Tartar mustard is English mustard fortified with cayenne pepper.