I believe the two words mean different things, and therefore the two tags should refer to different situations.
If I take my boss Lisa out to a fancy dinner when I know that bonus time is about to roll around, we will probably both employ correct etiquette in that we will chat pleasantly and put our napkins in our laps and eat with forks and knives. By taking her to a fancy dinner with the expectation that it will benefit me come bonus time, I am still behaving unprofessionally.
If my coworker Alejandro simply will not stop putting empty cartons of half and half back in the office fridge, he is breaching office etiquette. If I choose to confront him about this infraction by throwing an empty carton of half and half at his head while he is meeting with his biggest client, I am not behaving professionally.
Here are some suggestions for updated tag wikis for each of these concepts, just off the top of my head - feel free to edit or scrap:
Office etiquette covers the details of working day-to-day in a shared space with other people. Your office-mates may not work on the same projects as you, or even for the same company. Etiquette enables many people to occupy the same space day after day regardless of each person's company, department, or job function.
Professionalism has to do with conforming to the technical or ethical standards of your profession. It is related to your specific job function, industry, or company, and to the future prospects for your career. When not acting in a professional manner, you may lose credibility, opportunities for advancement, or even your position.