The Boss lady and I watched "Operation Petticoat" last night. It was just as silly as I remembered from 49 years ago. It "starred" Cary Grant and Tony Curtis. It "co-starred" people whose names, listed later, I did not recognize. Here the use of "star" and "co-star" (or participial forms) I derive from the "titles" shown at the beginning of the film.
When we speak of co-dependents, usually there is one, sort of starring, sick person, the family alcoholic or whatever. Around him or her cluster people who have adopted pathological ways of acting in response to his illness. At least that's the way they were teaching it a couple of decades ago. Those people with the "secondary" sickness are the "co-dependents".
Tell me how your dictionary works. When there are multiple definitions and usages do they post the least important ones first? Or, is that just your way?