I have long understood language from a neuroscience perspective is a means of sharing thoughts. If you see a car there is a cluster of neurons that light up saying 'car'. Apparently the same thing happens if you remember a car. Language taps in to that memory aspect and lights up the same associations.

Thus, the word Happy is the abstract feeling/memory of being happy and can have different but related meanings to everyone. Ditto, stop, gerund, pi etc.

IMO, abstractions past that point have more to do with redundant encoding than anything else.