A noun used to describe another, and standing in the same part of the sentence with the noun described, is called an Appositive, and is said to be in apposition: — externus timor, maximum concordiae vinculum , iungēbat animōs (Liv. 2.39) , fear of the foreigner, the chief bond of harmony, united their hearts. [Here the appositive belongs to the subject. ] quattuor hīc prīmum ōmen equōs vīdī ; ( Aen. 3.537 ), I saw here four horses , the first omen. [Here both nouns are in the predicate. ] litterās Graecās senex didicī ; ( Cat. M. 26 ), I learned Greek when an old man. [Here senex , though in apposition with the subject of didicī , really states something further: viz., the time , condition , etc., of the act ( Predicate Apposition ).]