Guessing that the reason that you get hits on parts of synonyms is that you are actually searching values on the product?
But I am not able to reproduce the issue, I tested with the steps below and was able to add abc as a synonym for arm071:
- Adding “arm071” to a product description
- Verify search works for “arm071”
- Add synonym
- Search for “abc” now give a hit for the arm071-product
