Use lair when you want to describe a hideout or dwelling for animals or, figuratively, for people. A lair often conveys a sense of wildness or primitiveness, and it frequently has a connotation of shelter or retreat. You might encounter this word in storytelling, particularly within the fantasy genre or when describing the habitats of wild creatures.

The word layer is versatile and applies to any context where items or substances are stacked or arranged one on top of the other. It features prominently in discussions about clothing, geology, art, and even psychology. When you use layer, you are drawing attention to the stratification or the incremental build-up of something, be it tangible or abstract.

In summary, lair is a noun that describes a secret or private place where an animal or person seeks solitude or security, whereas layer can be a noun or a verb that refers to a stratum of substance or the action of arranging substances sequentially. The distinction lies in lair's specific association with habitation and concealment, compared to layer's broader use in indicating levels or tiers of various materials or concepts. Selection of the right term depends on whether the primary focus is on refuge and retreat, or structure and arrangement.