'English Horn' is a fifth lower than oboe, so it's about 50% longer. It also has a bend near the top, and the bottom looks as if it is about to lay an egg. It is effectively an alto oboe. It's a transposing instrument, sounding a fifth lower than printed (so the fingering is the same as the oboe).
However the American name for it is based on a misunderstanding. The French name (also used in the UK) is 'Cor Anglais' - apparently 'English Horn'. In fact the French word was spelled wrong centuries ago and it should be 'Cor Anglé' - 'bent horn'. There is nothing English about it anyway. Players in the UK invariably refer to it simply as 'cor'.