Bad teacher

Some of the guys in my last class today wanted to know what the word tadpole meant. I drew one on the board. My drawing looked like a comma, only bigger, and wasn't very helpful, so I also explained that it wiggled around in ponds and later grew legs. I could not tell them that it grew up to be a frog, because that was the answer to the quiz question they were doing, and I knew that.

They understood what I meant, and were able to answer the quiz question correctly. (It was one where the question was harder than the answer.) Then they chatted about tadpoles and frogs a bit.

After a while one of them stuck his hand up again, and wanted to know what the word was for the tadpole that had started growing legs but wasn't quite a frog yet.

"Tadfrog", I said, before I could stop myself.

"Tadfrog ... tad - frog ... Oh, I SEE!" he said, and turned to tell his friends.

"Nonono! STOP!" I said. "It's not a real word!"

He stared at me in amazement.

"Sorry," I added, and he started laughing disbelievingly.

"Tadfrog is not a real word?" he asked. "Why not?"

"I don't know," I said helplessly. "I just made it up. Check your dictionary."

He did, and confirmed that it was not a real word. Then he taught it to his friends anyway, and tricked them into believing it, then told them the truth. "Ha ha ha, tadfrog!" they laughed, and I told them to PLEASE forget it, it's NOT A REAL WORD, and there IS no real word for a tadfrog, at least not one that I know. But I caught them later teaching it to other students and then laughing at them for believing it. They seemed to find the word funny because it made perfect sense and yet was not real.

Now I am afraid it is going to be the only new word from their year of classes with me that they will never forget.

(I just did a Google search on tadfrog and notice that it gets 97 hits. I retrospectively blame Google.)