areola

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A small ring of color around a center portion, as about the nipple of the breast or the part of the iris surrounding the pupil of the eye.
• noun A small space or interstice in a tissue or part, such as the area bounded by small veins in a leaf or the wing of an insect.

from The Century Dictionary.

• noun A tessellation in the thallus of some lichens.
• noun In entomology, a small, generally angular, inclosed space on a surface, as the spaces between the veinlets in the wing of a dragon-fly, or pale spaces between dark lines which form a network. Also areolet.
• noun In botany, a term sometimes used to designate the meshes of cellular tissue or little distinct angular spaces on a surface.
• noun In anatomy: Any little cell, area, or space; especially, one of the small interstices in the meshes of areolar tissue and the like, or among minute interlacing vessels, as capillaries. The colored circle or halo about the nipple of the human mammary gland, pink in virgins, and brown of various shades in women who have borne children. The red ring of inflamed tissue surrounding a pustule. Hence, figuratively
• noun An aureole.
• noun In decorative art and manufacture, any plate, tile, or flat panel.
• noun Also areole.

from the GNU version of the Collaborative International Dictionary of English.

• noun An interstice or small space, as between the cracks of the surface in certain crustaceous lichens; or as between the fibers composing organs or vessels that interlace; or as between the nervures of an insect's wing.
• noun (Anat. & Med.) The colored ring around the nipple, or around a vesicle or pustule.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun anatomy The colored circle around a nipple, more exactly known as areola mammae.
• noun anatomy Any small circular area that is different from its immediate environment such as the colored ring around the pupil of the eye (iris) or an inflamed region surrounding a pimple.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun small circular area such as that around the human nipple or an inflamed area around a pimple or insect bite
• noun small space in a tissue or body part such as the area between veins on a leaf or an insect's wing