It's worth noting again that even when a Spanish word does not have a definition in the Spanish-English page or even in the Spanish-Spanish page (reached by clicking on Definición), it may still have a "Definición RAE" --meaning the Diccionario de la Real Academia Española. This word is a good example; clicking on that menu selection gives you the following:
raleo.
1. m. Hond. En algunos cultivos, como el del frijol y el del maíz, acción de arrancar las plantas que han nacido muy juntas.
Under ralear, you'd find a lot more information in the DRAE.
Cheers.