Part of Speech-Noun

Definition-a genus of the family Equidae that comprises the horses, asses, zebras, and related recent and extinct mammals

Source–http://www.merriam-webster.com/medical/equus?show=0&t=1387334176

Encountering of Word-I was beginning to read a book by the name of “Equus” and i did not know the meaning of this tittle.

Understanding-I know see that this meaning of the word goes hand in hand with what the book is about, which is horses.