Physics and forces

The thirty-third entry is a dilatação, and the English word that offers itself is not the one a bridge engineer uses. Portuguese puts a dilatação wherever something grows larger, and the ordinary case is heat: A dilatação explica a junta na ponte. English calls that « expansion » and nothing else — thermal expansion, an expansion joint, an expansion tank, a coefficient of expansion. « Dilation » exists, and it comes from the same Latin verb dilatare, to make wide, but it has been left holding a short and specialised list: a pupil dilates in the dark, a cervix dilates in labour, and time dilates near the speed of light. The older spelling « dilatation » survives in medical writing and almost nowhere else. So « the dilatation of the rail » names nothing at all, and « the dilation of the metal » reads like an eye test. One relative has drifted further still and is worth knowing precisely because it will never turn up in a physics text: « to dilate on a subject » is to speak about it at length, the only place where the word still stretches anything in everyday English.