this was started with the haber process to harvest the nitrogen out of the air. the only other large scale process that does this is nitrogen fixation by legumes (actually bacteria in legume nodules), bacteria etc. first used as munitions by the germans, it later allowed the world to adopt corn as a feedstuff.
anhydrous means without (an) water (hyd )is converted to NH4+ in the soil, and since it is positively charged, it binds to the soil if there is enough clay in it. it is typically not applied to soils high in sand or pH as it is lost to the atmosphere.
one of the best investments i ever made in college was a latin root word dictionary. it helped me memorize definitions of words since essentially each syllable had a definition.