Every dictionary will tell you that concrete means concreto in Spanish. That is perfectly correct. The problem is that it also means hormigón, that is used for building. So if you’re talking about cooking, or medieval architecture, or anything else, it is best not to ask for a concrete example- !un ejemplo en hormigón! Very definitely, you must avoid sentences like We’ll meet on Tuesday, in concrete at ten o’clockNos vemos el martes, a las diez en hormigón. The other English words that are synonyms of concrete (concreto) are exact, precise, or specific.