The English language is full of synonyms (words that mean the same). The British Isles were invaded by the Anglo-Saxons, who brought their language. Then we were invaded by the Normans (pictured), and French was the official language until the year 1600. Educated people learned Latin and Ancient Greek so that they could read classical literature, and imported a lot of Latin and Greek into the language. That's why we often have a choice between a Latin, Greek or French word from the educated establishment, and an Anglo-Saxon word as used by the common people: between a word that sounds official and impressive, and one that sounds warm and everyday. Would you rather someone was amicable, or friendly?
Official words tend to have many syllables, with endings like "-atively" and "-ification". If you want to sound informed, domineering, impressive and pompous, and if you want to disguise your meaning, choose from the left-hand column. If you want to sound matey and get your meaning across, choose Anglo-Saxon words from the right.
previously, subsequently/earlier, later
More Latin here.