Verb
derich (third-person singular simple present deriches, present participle deriching, simple past and past participle deriched)
(aviation, rare) To make the air–fuel ratio (of a jet engine or a carburetor) leaner (less rich).
Synonyms: lean, disenrich
However, some of Holbein's other portraits of Steelyard merchants, for example that of Derich Born, concentrate on the naturalness of the face. Source: Internet