Comprehensive lists of words beginning with the letter B are available at the Collins Dictionary website. Words on the site are arranged in sequential alphabetical groups, starting with the letter "b" in the first group and ending with "BZ," the internet domain name for Belize, in the last. Expert definitions for any of these words can be viewed by clicking on them.
A number of other lists of words beginning with the letter B restrict their content to a specific theme. For example, at the Phrontistery website, there is a list of "unusual" words beginning with the letter B. These include: Barbigerous (bearded), Bathykolpian (deep-bosomed), Beerocracy (government by brewers), Birl (to spin a log by walking on it), Boeotian (stupid or dimwitted), Boggart (monster or ghost), and Bushwa (nonsense).
A themed list at the Colorado State University website displays animals beginning with the letter B. These include both well-known species, such as baboons, badgers, butterflies, boas, bats and bears, and some perhaps lesser-known species, such as bustards, bandicoots, bonteboks, boubous and bushbucks. Many species on the list are blue, black or brown variations of animals that do not otherwise begin with B, hence their inclusion. Examples of these include the black swan, black-faced kangaroo, blue catfish, blue-footed booby and brown pelican.