Gain a better understanding of medical terminology by searching our dictionary of more than 1,300 terms.


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  • menarche

    A woman’s first menstrual period.

  • membrane

    A thin layer of tissue covering an organ.

  • melena

    Black-colored feces caused by the presence of blood.

  • melasma

    Dark coloring of the skin often seen during pregnancy and at menopause. Also occurs in Addison’s disease.

  • melanoma

    A dark-colored tumor, especially malignant melanoma, that is a form of skin cancer that can spread from one part of…

  • melanin

    A brownish-black pigment normally found in skin, hair and parts of the eye.

  • melancholia

    A mental state characterized by extreme sadness. A severe form of depression.

  • meibomian gland

    A type of gland of the eyelid’s inner surface. Inflammation of a meibomian gland can produce a swelling called a…

  • medulla oblongata

    The part of the brain just above the spinal cord that includes the control centers for breathing, circulation and…

  • medulla

    The inner part of an organ. The adrenal medulla is the center of the adrenal gland where epinephrine (adrenaline) is…

  • mediastinum

    The tissues and organs located directly behind the sternum between the lungs. Contains the heart and its large vessels, the…

  • median nerve

    The nerve that stimulates some of the muscles of the hand and wrist.

  • meconium

    The greenish fecal matter in a fetus, forming the first bowel movement of a newborn infant.

  • Meckel's diverticulum

    A sac that may form in the small intestine, present at birth.

  • measles

    A highly contagious viral disease occurring most frequently in childhood and characterized by small, red spots on the skin, high…

  • maxillae

    The pair of bones forming the upper jaw.

  • masturbation

    Sexual self-stimulation.

  • mastoiditis

    An infection of the mastoid bone that can cause redness, warmth, swelling and pain behind the ear, sometimes with drainage…

  • mastoid

    A bony, rounded projection of the skull located behind each ear.

  • mastitis

    Inflammation of the breast.

  • mastectomy

    Surgical removal of the breast.