Lubricants and tribology

The eighteenth entry is la stabilité à l’oxydation, and the little word in the middle is the one an English reader will get wrong, for the good reason that English never had to choose it. « Oxidation stability », « shear stability », « viscosity index », « drop point »: all four are built by setting one noun in front of another and saying nothing whatever about how they hang together. French cannot do that, and the preposition it is forced to supply carries a meaning of its own. À names what the property is measured against, the enemy it holds out against: la stabilité à l’oxydation, la stabilité au cisaillement, la résistance à l’usure, la résistance à la corrosion. De names what is being counted, or what the thing is part of: l’indice de viscosité, l’épaisseur du film, le point de goutte, la classe de propreté. The test is whether the second noun is an adversary or a quantity. Getting it wrong leaves a phrase that still parses, which is why nobody catches it: la stabilité de l’oxydation quietly hands the stability over to the oxidation itself.