Architecture and building history

The twentieth entry is o átrio, and the English word beside it belongs to a small class that has never settled its plural. « Atrium » came into English straight from Latin, where atrium was the open hall at the centre of a Roman house, and it brought its Latin plural with it: « atria ». That form is compulsory in anatomy, where the two upper chambers of the heart are « the atria » and nothing else is written. In architecture, where the word now names the glazed hall a modern office block is built around, both « atria » and « atriums » circulate. English does this with every borrowed neuter: « stadium » gives « stadia » in athletics writing and « stadiums » in the sports pages, « forum » has gone over almost entirely to « forums », and « medium » split in two, « media » walking off to become a word of its own. The rule behind the muddle is worth stating: the more ordinary a borrowed word becomes, the more likely it is to take the English plural. O átrio has none of this trouble, and says os átrios.