Espada, as far as i know, Is the Spanish word for "Sword", so they're essentially Aizen's weapons.
A few other terms you might like to know. Arrancar means 'Rip off' or 'Tear off' in Spanish, in reference to their masks. 'Cero' is Zero (pretty easy to guess) and 'Gran Rey Cero' is 'Great King Zero'.
Hollows are Spanish themed (if you didn't guess), Quincy are German and Shinigami are of course, Japanese.