Radiotherapy

The twentieth entry is la reazione cutanea, and the noun that opens it does a job in Italian that « reaction » never does in English. On the ward the two words match exactly: la reazione cutanea is the skin reaction, una reazione allergica is an allergic one, and la reazione acuta stands two entries above. Take the same noun out of the clinic, though, and put a in front of it, and it stops describing a response altogether. Un aereo a reazione is a jet aircraft, il motore a reazione is a jet engine, and volare a reazione is to fly by jet. The picture behind that is Newton rather than the pharmacy — the engine drives gas backwards and the gas drives the aircraft forwards — and Italian built a whole vocabulary on it, where English reached instead for the thrown stream in the word « jet ». A third sense is political: la reazione, with the article and no complement, is the reactionary camp, and un reazionario belongs to it. So the noun on its own settles little, and the small word standing in front of it settles everything.