1. (in botany) The continuous waxy layer that covers the aerial parts of a plant. Composed mainly of cutin, it is secreted by the epidermis and its primary function is to prevent water loss.

2. (in zoology) A layer of horny noncellular material covering, and secreted by, the epidermis of many invertebrates. It is usually made of a collagen-like protein or of chitin and its main function is protection. In arthropods it is also strong enough to act as a skeleton (see exoskeleton) and in insects it reduces water loss. Growth is allowed by moulting of the cuticle (see ecdysis).