what does idhgaam noon sakeen means?

Question
what does idhgaam noon sakeen means?
Answer
Idghaam means merging.  So when a letter has "idghaam" into another, it merges into second letter so that what is heard is the second letter, empahisized with a shaddah (double).  Noon is the Arabic letter  .  Saakinah (you wrote sakeen, but the correct word is saakinah) means voweless.  So idghaam noon saakinah means, the merging of the non-voweled letter into the letter which follows it.

For more information please see:
http://www.abouttajweed.com/the-noon-saakinah-and-tanween/merging-of-the-noon-saakinah-and-tanween-p-2.html
http://www.abouttajweed.com/the-noon-saakinah-and-tanween/merging-of-the-noon-saakinah-and-tanween-p.html