English vocabulary has endless potential for growth and innovativeness. Due to the english language being so vast in words and phrases, the potential size of english vocabulary is galactic. Since new english words are being created everyday, english vocabulary can potentially be infinite.
A person's innate and natural vocabulary is usually a product of their environment. It's only natural a person's vocabulary absorb all of the words they are accustomed to hearing and seeing on a daily basis. In a lot of cases, friends/people who hang around each other often speak alike and share a similar vocabulary due to being exposed to similar words and speech patterns. Despite that, each person's vocabulary when large enough can still be unique since the choice of words to be utilized can be based on preference.
Idioms are a significant part of english vocabulary. Idioms are sayings/expressions that convey figurative meanings. The english language consists of several thousand idioms. Idioms can be easily misconstrued by people who are not familiar with the idiom they see or hear. Even understanding every word in the idiom isn't enough to know the true meaning behind the idiom since idioms are not meant to be taken literally. Idioms are a big part of english vocabulary because people pick and choose the idioms they want to utilize in their speech. Idioms are not at all necessary but using them is an interesting and unique way to convey a meaning rather than use the traditional literal way of conveying that same meaning.
Slang words are another part of english vocabulary. Slang is definitely something that emanates from environment and atmosphere more than anywhere else. The invention of new slang can easily occur among a small group of people and propagate among broader groups via hearsay. Slang is conventionally used in informal and casual conversations. The english language consists of millions of slang words. Since the amount of slang words available in the english language is so vast and slang is also something that isn't really necessary to convey an intended meaning that can be conveyed with traditional english, slang is also something that can be picked and chosen to be a part of one's english vocabulary.
Expletives are a component of english vocabulary that a lot of people either use, or are against the use of. A lot of people who are against the use of expletives have a hard time not using expletives themselves sometimes depending on the situation they are in. While expletives have no meaning and are unnecessary, they are usually used to add exclamation to what is being said. Expletives can usually take the form of swear words or even certain traditional english words that lose any meaning they had when being used as an expletive.
Aside from traditional english words and phrases, a large portion of native english speakers utilize both idioms and slang with their english vocabulary. Since all of the above(english words, idioms, slang words and expletives) are perpetually being created, the english language as a whole grows at a rapid rate. This makes the extent and style of english vocabulary unique in delivery and brobdingnagian in size.