So I will admit that I don't know a lot about how elastic search works under the hood, but I can describe how ours does. Under the hood we use a large language model called BART which has 2 key benefits: 1. It has more "general knowledge", so it doesn't just search for semantic similarity between the text and tags you provide. This makes the tagging more accurate. 2. This model can be fine-tuned fairly easily for specific use-cases or on more recent datasets. For example, if you have your own taxonomy that you'd like to categorize certain text by - this is popular amongst advertisers who need to place ads on specific types of content, and e-commerce companies that need to categorize products on their site in an easily separable way - it's pretty straightforward to teach this model.

The synonyms question is a good one - so far, we've found that adding them here isn't really necessary as they'll all present similar scores.