noun, plural: trichomes
(botany) An outgrowth (hair-like or scale-like) from the epidermal cell
(microbiology) A hair-like structure on the surface of certain microscopic organisms
The term trichome comes from the Greek trikhōma, which in turn is from trikhoun (meaning “to cover with hair”) or from thrix (meaning “hair”). It is used to generally pertain to a hair- or bristle-like outgrowth or extension on the cell surface. Thus, it may pertain to the hair-like outgrowth on the surface of the cells of certain microorganisms, algae, and plant cells. The term trichome is more commonly used in plants where it is used to refer to any of the various outgrowths on the epidermal cells. Many of these outgrowths are hair-like, others are scale-like. Some of them may be glandular, secreting oils and certain substances.
Trichomes have various functions. They curb the rate of transpiration (i.e. the loss of water through the stomata), reduce the effect of heat from sunlight (such as by reflecting solar radiation thereby lowering plant temperature), confer a defense mechanism against insects and other small herbivores, and protect inner tissues from mechanical injuries.
Botanists use the terms pubescent and glabrous to describe the surface of plant parts. In particular, a plant organ with trichomes is described as pubescent whereas one lacking trichomes is described as glabrous.