What is the pulpy fruit of Persea gratissima, a tree of tropical America. It is about the size and shape of a large pear; -- called also avocado pear, alligator pear, midshipman's butter called?

avocado — The pulpy fruit of Persea gratissima, a tree of tropical America. It is about the size and shape of a large pear; -- called also avocado pear, alligator pear, midshipman's butter. (Webster's 1913.)