A person who currently holds the title in a sport — that is, the reigning champion. It is an American sports-writing word, and quite old-fashioned; you would find it in a boxing report from the middle of the last century ('the heavyweight titlist') more than in today's news, where 'champion' or 'title-holder' is normal. It works like a synonym for 'champion', but with one shade of difference: it points at the title as a thing being held, which is why it fits sports where a belt or a crown passes from one person to the next — boxing, wrestling, golf. Newspapers liked it partly because it is short and fits in a headline. Your students will almost never need to produce this word; recognising it in an old article is enough.

衛冕者、（現任）冠軍（美式體育報導用語，較舊）