Words are defined by people. They don't change on a whim. Most words in English come from other languages, particularly French or Latin, but they are imported from many other languages.
The purpose of a dictionary is to standardize spelling and pronunciation. They do not define words. They often given an example of the usage of a word (sometimes inaccurate!), but they do not define them. Dictionaries don't even agree with each other! No dictionary owns any word.
The study of the origin of words is called 'etymology'.
Some words are defined by philosophy, such as 'real', 'religion', and 'science'. Some words, like 'mathematics' is simply created and built up over time.
The word 'shill' was created in 1911 and referred to their use in circuses, to lure customers. In a casino, that is exactly their job. To lure customers into a poker game that looks busy, but isn't yet. As the game fills up, the shills bow out of the game, always leaving a couple of seats open for more customers to sit down and play. After all, nine people just don't walk up at once in a casino to play poker, particularly in the morning to afternoon, when you are trying to get games started for that evening.
In a casino, shills must identify themselves if asked.
It's not an insult. NoName is trying to use it as an insult. Shills have a specific purpose for being there. They benefit the players, they benefit the casino, and they benefit themselves as dealers.