pilo-, pil-, pili- +
Don't confuse the words in this pilo-, pil- group with the pil- or "plunder, heap up" unit.
2. Bearing or producing hair; the outermost layer of root or epiblema that gives rise to root-hairs.
2. An involuntary erection or bristling of hairs due to a sympathetic reflex usually triggered by cold, shock, or fright, or due to a sympathomimetic agent.
"Goose bumps" (American English), also called "goose pimples", "goose flesh" (British English), "chicken skin" (Hawaiian Pidgin), or cutis anserina, are the bumps on a person's skin at the base of body hairs which involuntarily develop when a person is cold or experiences strong emotions; such as, fear. The reflex of producing goose bumps is known as horripilation or pilomotor reflex. It occurs in humans and in other mammals.
Piloerection starts when a stimulus such as cold or fright causes a discharge from the (involuntary) nervous system that triggers a contraction of the little arrectores pilorum muscles. Contraction of these muscles elevates the hair follicles above the rest of the skin so the hair seems to "stand on end".