كَالْعِهْنِ

كَالْعِهْنِ is a phrase (شِبْهُ الجُمْلَةِ), a compound consisting of a particle of pulling down (preposition) and a genitive noun

الْعِهْنُ is the natural state of this definite noun and it changes to كَالْعِهْنِ due to the preposition كَ that precedes it

PhraseParticle/NounNoun Particle 
شِبْهُ الجُمْلَةِجَارٌ وَمَجْرُوْرٌاسْمٌ مَجْرُوْرٌحَرْفُ جَرٍّ
PhraseCompoundGenitive NounParticle of pulling down
  
like woolكَالْعِهْنِ=الْعِهْنِ+كَ
like woolwoollike
Surah/Below are the 2 verses in the holy Quran containing the genitive particle and genitive noun compound كَالْعِهْنِ
Verse
70-9
101-5and the mountains will be like teased woolوَتَكُوْنُ الْجِبَالُ كَالْعِهْنِ الْمَنْفُوْشِ