I’ve recently noticed the word “pony” being overused, in books and conversation. Sometimes it seems highly unlikely that ponies are so prevalent in the setting.
So I was thinking. Maybe there is a region in which “pony” is colloquial for “horse”? And why would it become colloquial in the first place?
TL;DR: In the US, you will see large, adult horses referred to as "ponies" in association with:
- Horse-racing, especially gambling on horse races.
- Young women and girls, and stories about young women and their horses.
I don't know about region, but at least in the US there are two contexts where "ponies" can mean "horses, generally" (regardless of size or age).
The first is horse-racing, and particularly the gambling associated with these races. From Oxford Dictionaries:
1.1 (the ponies) informal, chiefly North American Racehorses: 'he had been playing the ponies on the side'
"Playing the ponies" is an idiom meaning "betting on a horse race"; it is even the title of a Three Stooges movie about horse racing. By extension, people talking about horse racing will just say "the ponies" even though they're often talking about huge adult horses.
The other realm in which "ponies" can be used for horses of all types is when referring to the stereotypical love of girls and young women for horses. For example, National Velvet (both novel and film) is often described as one of the most influential examples of the "pony story" (see, for example, the International Companion Encyclopedia of Children's Literature) even though it actually features a full-size, adult horse suitable for steeplechase racing.
This association is partially due to the fact that young girls would be more likely to ride a pony than a full-size horse, and thus actual ponies are often involved. The term "pony tale" for stories featuring young female equestrians and their horses is probably especially attractive since a ponytail is a hairstyle sometimes associated with girls and young women. Associating "ponies" with the horses of women and girls, regardless of whether the term otherwise applies, also fits with the sometime-practice of equating "feminine" with "young and small". This particular usage has likely also gotten a boost recently from the My Little Pony franchise.
"Pony" is indeed often used as an umbrella term for horses, or rather more specifically, a young horse. In fact this usage is so common that many people fall under the mistaken belief that pony is just another word for a foal.
That said, it should be safe to assume, given the technical definition of pony as well as the colloquial understanding, that if someone uses the term "pony" they are likely speaking about a small horse. Of course, there are also those that use the word for any horse, in which case you'll have to rely on context for more information (or ask them directly "what kind of horse").
So, in short, your suspicion that the word is being over/innaccurately used is correct. As far as the actual line of thinking that led to this colloquial definition, I couldn't find any reliable sources explanating it, so it's anyone's guess. My theory would simply be that most people (in the US at least) are only passingly familiar with horses, and so wouldn't know that there are specific kinds horses known as ponies, and thus when hearing the word simply form the association "small horse = pony = young horse" etc.
but of course, this is just speculation
Formally, pony refers to specific breeds of horses of small varieties. Informally it is often used for horse racing, any small horse, young horses, diminutives for a specific horse or a playful horse or just horses in general.
"Pony" could also be used to show affection. We often use the name of the younger version of the animal to show love. Baby, kitten, puppy and other words are used to refer to adults of these different animals. With other people this manner of speech is called baby talk.
