The word "sombre" means dark, dull, or melancholic, often used to describe a mood or atmosphere. The closest synonym is "gloomy," which also refers to something dark, depressing, or cheerless. Here's the analysis of the options:
- Causing sleep: Refers to something that induces sleep, not related to "sombre."
- Squalid: Refers to something dirty or unpleasant, not related to "sombre."
- Gloomy: Refers to something dark, depressing, or melancholic, which is exactly the meaning of "sombre."
- Malicious: Refers to harmful intent, unrelated to "sombre."
Therefore, the correct answer is "gloomy".