Steven Price's Horseman's Illustrated Dictionary is excellent and poor at the same time.

When I first looked at it, I was impressed. It's attractively laid out, comprehensive and well-illustrated. Here's your source for the meaning of words used in the context of horses.

Are you an English rider who has wondered what western riders meant by a leak? Or a western rider who has wondered what an in-and-out was? This book will tell you. It will also tell you that Buttermilk was Dale Evan's horse and that Federico Caprilli was an Italian horseman credited with the development of the forward seat.

Why do I say it's poor? Unfortunately, a few of the definitions are misleading, if not wrong.

However, overall, Price's dictionary is well worth owning. The book's strength lies in its explanations of ordinary terms that horse people use all the time -- the jargon of the equestrian world. For specialized information, you need to go to books written by experts in their field.