Hilar: of, relating to, or located near a hilum.
"Hilarous", then, would be the condition of being located near a hilum.
And a hilum is, of course, a scar on a seed (as a bean) marking the point of attachment of the ovule.
I'm sure a bean joke can be wedged into this thread somewhere..... Just as a face-saving measure.
12-hour workdays, 120-degree heat - it's taking its toll. And I think I have a hilum on one of my typing fingers.
That's my excuse and I'm stickin' to it! :)