A Rash of Good Luck

Roger: "What happens when you cross a four-leaf clover with poison ivy? You have a rash of good luck." And then, unforgivably: "I was just itching to tell someone."

Two puns. I shall take them one at a time, like a man defusing a bomb he built himself.

The first is rash. Last week, with the animal crackers, we had a homonym — two unrelated words that merely look alike. This is subtler, and frankly better bred: polysemy — one word whose two meanings are actually cousins. A rash is what the poison ivy gives you. A rash of something — a rash of burglaries, a rash of good luck — is a sudden spate of it. And the second sense grew straight out of the first: a rash breaks out and spreads, so an outbreak of events quietly borrowed the word. Same root, two branches. The clover supplies the good luck, the ivy supplies the rash, and the pun is simply the one word that can shake hands with both parents at once. That, grammatically, is the entire job description of a crossbreed joke.

Then itching to tell someone — and he does it again. To be itching to do a thing is to be restless to do it: another idiom that crawled out of a physical symptom. The body is forever lending its sensations to our impatience — we itch to leave, we hunger for success, we ache to be believed.

Sam: So the takeaway is: the joke is about a rash, and explaining it gives me one.

Roger: Two symptoms, one etymology. I call that value for money.

When one word grows a second, related meaning, that's polysemy — Pillar 8, word choice.