1. Plaster: This is the most common meaning. It refers to the material used for plastering walls and ceilings, and also for making casts for broken bones.
2. Gypsum: This refers to the mineral form of hydrated calcium sulfate, which is the main ingredient in plaster.
So, the meaning of "plaitre" is essentially plaster or gypsum, depending on the context of the sentence.
For example:
* "Le mur est recouvert de plaitre." (The wall is covered in plaster.)
* "Le médecin a mis un plaitre à sa jambe cassée." (The doctor put a plaster cast on his broken leg.)
* "Le plaitre est un matériau de construction important." (Gypsum is an important building material.)