IMHO, leo is better than dict.cc but it is also community edited. I suggest to go with pons. Generally, I'm a big fan of crowd work but compiling a dictionary really requires expertise. There are so many subtleties to consider (which meanings are distinct, which words are colloquial, slang or socialects, which expressions are used only in certain regions, what differences are there between dialects, which usages are outdated, and so on and on...) and you have to work very systematically and consistently - laymen simply can't do this. It's really a different task than - say - writing articles for Wikipedia since you have to have a good and complete understanding of the whole language.
In British English "The senior works" doesn't make any sense. We talk about a senior citizen / pensioner / old (or elderly) person (or man). "The pensioner works" should also be accepted, i believe.
In german is there a distinction between Senior and Rentner?
Would "Der Rentner arbeitet." would have a different meaning?