Riddle
Here’s a riddle I’ve been pondering for a while, so I thought I might as well post it before I head to the dentist.

“What five-letter word can you add a letter to get a six-letter word, another letter to get a seven-letter word and another letter to get an eight-letter word? What’s unusual about the four words?”

I’ve got it up to seven. But not eight. Any ideas?