natural object - an object occurring naturally; not made by man

scale - a flattened rigid plate forming part of the body covering of many animals

shell - the hard largely calcareous covering of a mollusc

test - a hard outer covering as of some amoebas and sea urchins

body covering - any covering for the body or a body part

sheath, case - an enveloping structure or covering enclosing an animal or plant organ or part

integument - an outer protective covering such as the skin of an animal or a cuticle or seed coat or rind or shell

blanket, mantle - anything that covers; "there was a blanket of snow"

crust, encrustation, incrustation - a hard outer layer that covers something

envelope - a natural covering (as by a fluid); "the spacecraft detected an envelope of gas around the comet"

indument, indumentum - a covering of fine hairs (or sometimes scales) as on a leaf or insect

shell - a rigid covering that envelops an object; "the satellite is covered with a smooth shell of ice"

eggshell, shell - the exterior covering of a bird's egg

skim - a thin layer covering the surface of a liquid; "there was a thin skim of oil on the water"

slough - any outer covering that can be shed or cast off (such as the cast-off skin of a snake)

snowcap - a covering of snow (as on a mountain peak)

vesture - something that covers or cloaks like a garment; "fields in a vesture of green"

peridium - outer layer of the spore-bearing organ in many fungi

pericarp, seed vessel - the ripened and variously modified walls of a plant ovary

chlamys, floral envelope, perianth, perigone, perigonium - collective term for the outer parts of a flower consisting of the calyx and corolla and enclosing the stamens and pistils

theca, sac - a case or sheath especially a pollen sac or moss capsule

indusium - a membrane enclosing and protecting the developing spores especially that covering the sori of a fern

bark - tough protective covering of the woody stems and roots of trees and other woody plants