This is an Infographic on the names to describe various types of horse. I found researching this interesting. I am indebted to Desmond Morris, the author of the book HORSEWATCHING. The Infographic is deliberately compressed tremendously in terms of the information provided as there is limited space. I mention that because sometimes the evolution of a particular word such as “pony” has a particularly long and tortuous path (see below the infographic).
With respect to the word “Pony”. As mentioned in the Infographic, it originates in the Latin word “pullus” meaning foal. From this beginning it developed to pullanus meaning colt. In old French this became transformed into poulain and a small colt was given a special title poulenet. When the word reached Scotland it was pronounced (mispronounced) ‘pool-ney’. And then modified to ‘powney’. You can see the word gradually evolving. The word was associated to tiny Scottish horses found in the Shetlands and elsewhere. And about 200 years ago dictionaries began to refer to ponies as ‘little Scotch horses’. And so, the word “pony” latterly originated in Scotland.
I strongly recommend the book that I refer to in the first paragraph. In fact, I recommend all the books of Dr. Desmond Morris, a highly celebrated English zoologist, ethologist and surrealist painter, as well as a popular author.
Below are some more articles on horses.