Mechanical engineering and production

Late on this list stand le rodage and roder, and their root explains what the operation actually is. French took the verb straight out of Latin rodere, to gnaw, and English keeps three of its descendants in ordinary use: a « rodent » is a gnawer, something that « corrodes » gnaws away at metal, and a river that « erodes » a bank gnaws it out from underneath. Running an engine in is that same idea put to work on purpose — two surfaces are allowed to gnaw each other smooth under light load before anybody asks them to carry a full one. Hence le rodage dure les cent premières heures, and hence the figurative use, where a new team or a new show is en rodage, still wearing its rough spots down. One warning about the spelling, because the two words are neighbours on the page and strangers in the dictionary. Rôder, with the circumflex, comes from Latin rotare, to turn, and means to prowl: un homme rôdait devant l’atelier. That accent is the whole difference between running an engine in and loitering outside.