Think of two words, naming two things used for the same purpose - related to cooking. One is a modern-day, common word. The other is an unfamiliar word, dating back to the past,  Add the same letter to the beginning of both words. Now the common word is uncommon, and the uncommon word is common. What are the original two words, the added letter, and the two new words?

Answers:

The first two words are OVEN and OAST.
The added letter is C.
The second two words are COVEN and COAST.