Kiln قمين

In a dream it signifies worries, miseries and dubious matters. A gypsum kiln [the source reads "kiln of the two kinds", probably a copyist's error] signifies slandering scholars with evil speech, because of His saying, the Exalted:

ثُمَّ قَسَتْ قُلُوبُكُم مِّنۢ بَعْدِ ذَٰلِكَ فَهِىَ كَٱلْحِجَارَةِ أَوْ أَشَدُّ قَسْوَةً ۚ وَإِنَّ مِنَ ٱلْحِجَارَةِ لَمَا يَتَفَجَّرُ مِنْهُ ٱلْأَنْهَـٰرُ ۚ وَإِنَّ مِنْهَا لَمَا يَشَّقَّقُ فَيَخْرُجُ مِنْهُ ٱلْمَآءُ ۚ وَإِنَّ مِنْهَا لَمَا يَهْبِطُ مِنْ خَشْيَةِ ٱللَّهِ ۗ وَمَا ٱللَّهُ بِغَـٰفِلٍ عَمَّا تَعْمَلُونَ

“Then your hearts became hardened after that, being like stones or even harder. For indeed, there are stones from which rivers burst forth, and there are some of them that split open and water comes out, and there are some of them that fall down for fear of Allāh. And Allāh is not unaware of what you do.”

Quran 2:74 · Saheeh International

A kiln for fired brick signifies transgression, injustice and associating partners with God, because it is among the things the Pharaohs used. The kiln may also signify Hell and its people, and prison and its people and those imprisoned in it, like the bathhouse and its people.