Noun + de + noun (no article)

A "noun of noun" case happens when the second noun gives some information on the first noun's content, material or purpose:

• content: une bouteille de lait = a bottle of milk
• material: un pont de pierre = a stone bridge
• purpose: un couteau de cuisine = a kitchen knife.

As you can see, this French construction does not exactly match English where a noun can become an adjective if you place it in front of another noun. In French, you cannot use a noun as an adjective.

Written by Sitesurf@https://www.duolingo.com/comment/14079873$comment_id=14082490