Dictionary of Medical Terms

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

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All terms that start with the letter O
  • obesity

    Having too much body fat. A weight more than 20% above the normal range.

  • obsession

    An ongoing preoccupation with an idea.

  • obsessive-compulsive

    Marked by a need to repeatedly perform certain behaviors or rituals.

  • obstetrics

    The branch of medicine that deals with the care and treatment of women during pregnancy and childbirth.

  • occiput

    The back of the head.

  • occult

    Hidden from view.

  • occupational illness

    Any illness caused or aggravated by a person’s job.

  • occupational therapy

    Teaching useful skills to sick or handicapped people to promote rehabilitation and healing.

  • ocular

    Having to do with the eye.

  • odontalgia


  • olecranon

    The projection of the ulna (the larger of the two bones in the forearm) at the elbow.

  • olfactory

    Having to do with the sense of smell.

  • oligomenorrhea

    Light menstrual flow.

  • oligospermia

    A low number of sperm in the semen.

  • oliguria

    A condition characterized by an abnormally small output of urine.

  • oncology

    The study of tumors.

  • oophorectomy

    The surgical removal of an ovary.

  • ophthalmology

    The branch of medicine that pertains to the eye and its diseases.

  • optic neuritis

    Inflammation of the optic nerve, which connects the eye to the brain. Symptoms include pain with eye movement, blurred vision…

  • optical

    Having to do with vision.

  • optometry

    The practice of eye and vision care.