engaged in a specified activity as one's main paid occupation rather than as an amateur.
"a professional boxer"
synonyms: paid, salaried, non-amateur, full-time
"a professional tennis player"
Your point about "never full time admittedly" is an oxymoron. If you aren't full time then you aren't a professional?
There is no contradiction between:
1: "Professional" meaning that activity is your _main paid occupation_
2: Not working at full time.
A family member is working 40% as a musical teacher and 60% as a musician. I would consider him a "professional musician".
I know people who work 50% as bus drivers or nurses due to a medical condition, or due to taking care of kids or parents. I would still consider these "professional" bus drivers or nurses.
Not that "professional" has a lot of positive connotation to me. In my experience, professionals are prone to do any given job "good enough", while an amateur ("lover of") will often invest what seems like irrational amounts of time and money into getting things "as good as possible".
Granted, in professions such as photography, the line between professional and amateur, occupation and "lover of" is often blurred. People may do something for a living, yet invest more effort/money than what is required by their customers. Unlike more mundane occupations, perhaps? You don't often see bus drivers or nurses doing their thing for free for a decade before deciding to start charging by the hour?
-h