In a Word: Pulchritude

We all know what onomatopoeia is, even if we don't know it by name. It's when a word sounds like what it represents. For example, coo, boom, hiss, and shriek.

But what do we call a word that evokes the opposite of what it represents? Take the word pulchritude, for example. If I thought it were onomatopoeic, I would take it to mean something like vomitous, putrescent, or disgusting. But it's not. Quite not. If you don't know it already, pulchritude means beauty.

How can such a putrid-sounding word refer to something so lovely?

"Oh, honey! Your pulchritude is beyond reproach! Will you kiss me now?!"

I don't think so.