What does it mean to put a な after an い-adjective? For example, many Youtube videos are called begin "いいなCM", and a Japanese text book I have uses this sentence as an example:
この通りを行くと 大きな 交差点がある。
Go along this street, and you will find a large crossroads.
What is the meaning of this な? It is also unusual that the 大きい is missing the final い but the いいな is not. I cannot find it in my textbook or on using Google.