Not All Spanish Words Meaning "Worker" Are Created Equal
How Many Kinds of Workers Are There?
The most common words in Spanish that refer to a worker are obrero, trabajador, jornalero and labrador. Each has a certain sphere of usage that in many cases is not shared by the other. They all have feminine forms as well: obrera, trabajadora, jornalera and labradora.
The most generic word is trabajador. It is the word most used to refer to artisans, craftsmen or workmen. It is also the most common word used to express the Marxist concept of the proletariat; however, I have also seen, in Chinese translations of Marx and Lenin, the word obrero used as well (see below).
The word obrero is used to refer to skilled or semi-skilled workers, such as factory workers. The Spanish translation of the famous slogan of the International Soviet was often rendered using obrero: Obreros de todo el mundo, ¡uníos! (Workers of the World, Unite!)
It is easy for English speakers to say, mistakenly, unión for a labor union but the proper word is sindicato -- a word which in Spanish has no overtones of criminality.
When one wants to say that someone is a good worker, one says: Es buen trabajador or trabajadora.
The word jornalero refers to a day laborer, as in a handy man or hired hand.
The word labrador only is used to refer to farm or agricultural labor.
In addition, there are other words that one may encounter. In the US, the word bracero is used to refer to farm labor. The word ganapán is used in Spain to refer to someone who, as the word suggests earns his or her bread.
Here are some examples, with translations:
Los obreros salieron huelga ayer. The workers went on strike yesterday.
Mi tío fue jefe del sindicato de carpinteros. My uncle was boss of the carpenter's union.
Juana es muy trabajadora. Juana is a good worker.
Los jornaleros cobran por día. The day laborers charge by the day.
En la granja hay muchos labradores. There are a lot of workers on the farm.