Explosion protection

The fifteenth entry is a segurança intrínseca, and the adjective inside it is one an English reader uses weekly without ever picturing anything. « Intrinsic » comes from the Latin adverb intrinsecus, which meant on the inside; it is built out of a first piece meaning within and the old adverb secus, alongside, so what is intrinsic is what runs along on the inside. The word had a twin, extrinsecus, from without, and English kept that one too as « extrinsic », though it is now heard almost only beside its brother in a lecture on motivation. Everywhere else « intrinsic » has gone abstract: intrinsic value, intrinsic worth, intrinsic merit, always a quality that belongs to the thing itself and was not conferred on it from outside. This entry hands the word its body back. A segurança intrínseca is safety that lives inside the circuit, in the small amount of energy the circuit is allowed to hold, and not in a wall built round it — which is what the Latin adverb said in the first place, and the one place on this list where « intrinsic » can be read with a finger on the thing meant.