"good" is pleasure and "a good" produces pleasure/good.
I'm actually fine with that. I would turn that first part around, and say pleasure is good, a good produces pleasure. Sounds more natural, and pleasure logically precedes the concept of good. But I do not object to that.
"good" has multiple meanings
Does it really, though? I mean in a strict grammatical sense, that is obviously true. But all meanings of good that I can think of describe a thing that produces pleasure. Do you have an example in mind where that is not the case?
agathon ἀγαθόν good — often with a connotation with utility and advantage (for the agent), i.e. ‘good for’
All the proposed definitions for good that I've seen so far just introduce more terms that need to be defined, and at some point it's going to either become circular, or it has to come back to pleasure. I don't see any other way out. But, maybe I will be proven wrong.