Apologetics vs ecumenism vs evangelism

I've been struggling to understand the lines between these three activities for at least a year or two. Hopefully members will suggest and comment on authoritative definitions, but perhaps discussion of conflicts and questions would also be useful.

Perhaps a better starting point would be to ask for consensus, or clarification, on what is apologetics. Fr Hardon's pocket dictionary says the Greek origin meant defense, although Hardon gives a definition as the science (?) that aims to explain and justify religious doctrine.
I wish he'd just stopped there, and for the moment I think it's best to leave out his next comments.
I understand and support the value of defending our Faith against accusations and defamation. This certainly would usually include at least a bit of explanation and justification, but I wonder if the principal of apologetics generally is most effective when it involve response to specific provocation, rather than the more frequently (and perhaps appropriately) initiated evangelism and ecumenism, as well as teaching and preaching.