Talking about language in Portuguese

The twenty-third entry is a expressão idiomática, and the reason Portuguese needs two words where English needs one is that the obvious noun was already taken. Both languages inherited Greek idiōma, a peculiarity, a thing belonging to oneself, built on idios, own. Portuguese handed that noun the larger job: o idioma is a language, as in o idioma oficial or aprender um idioma novo, and it stands beside a língua as the slightly more formal of the two. English handed the same noun the smaller job. « An idiom » is a fixed expression whose sense cannot be read off its parts, so traduzir uma expressão idiomática palavra a palavra não resulta is best rendered with that one word rather than with « the idiomatic expression », which is correct and heavier than it needs to be. The trap is worth stating in both directions: « idiom » never names a language in ordinary English, and idioma never names a fixed expression in Portuguese. English keeps one further sense, the manner of a writer or a period, as in « the idiom of the late quartets », and that is as close as it comes to the Portuguese word.