obesity (ō-BĒ-sĭt-ē): Abnormal increase in the proportion of fat cells resulting in excess body weight for height.

obstetrician (ob-stĕ-TRISH-ăn): The person who specializes in the study of obstetrics and gynecology and are referred to as OB/GYN Obstetrics and Gynecology.

Obstetrics (ŏb-STE-triks): Medical specialty dealing with pregnancy, childbirth, and puerperium.

occipital lobe (ok-SIP-ĭt-ăl lōb): Region of the cerebral cortex directly beneath the occipital bone of the cranium.

occlude (ŏ-KLOOD): Block or close tightly.

oculomycosis (ŏk-ū-lō-mī-KŌ-sĭs): Abnormal condition of the eye caused by a fungus.

olfaction (ŏl-FĂK-shŭn): Special sense responsible for smell, which has a unique, direct connection to the cerebrum.

oligodendrocyte (ol-ĭ-gō-DEN-drŏ-sīt): Glial cell type in the CNS that provides the myelin insulation for axons in tracts.

oligohydramnios (ŏl-ĭg-ō-hī-DRĂM-nē-ōs): A condition where there is minimal amniotic fluid within the placental sac. Too little fluid can restrict the fetus from movement and growth.

oligomenorrhea (ŏl-ĭ-gō-mĕn-ō-RĒ-ă): Infrequent or irregular periods.

oligoovulation (ol-i-gō-ov-yŭ-LĀ-shŏn): Infrequent ovulation.

oligospermia (ŏl-ĭ-gō-SPĔR-mē-ă): Condition of scanty sperm.

oliguria (ŏl-ĭg-Ū-rē-ă): Scanty urine (output).

omentum (ō-MENT-ŭm): Fatty tissue that stretches over the abdomen, plays a role in immune response and the growth of certain cancers.

omphalitis (ŏm-făl-Ī-tĭs): Inflammation of the umbilicus.

omphalocele (ŏm-FĂL-ō-sēl): Herniation of the umbilicus.

onychocryptosis (ŏn-ĭ-kō-krip-TŌ-sis): Abnormal condition of a hidden nail.

onychomalacia (ŏn-ĭ-kō-mă-LĀ-shă): Softening of the nails.

onychomycosis (on-i-kō-mī-KŌ-sĭs): Abnormal condition of a fungus in the nails.

onychophagia (ŏn-ĭ-KŎF-ă-jē): Eating the nails (nail biting).

oocyte (Ō-ŏ-sīt): Female gamete.

oophorectomy (ō-ŏ-fŏ-REK-tŏ-mē): Surgical removal of the fallopian/uterine tubes.

oophoritis (ō-ŏf-ō-RĪ-tĭs): Inflammation of the ovary.

ophthalmalgia (ŏf-thăl-MĂL-jē-ă): Pain in the eye.

ophthalmia neonatorum (of-THAL-mē-ă nē-ŏ-NĂ-tōr-ăm): Conjunctivitis in newborns (severe).

ophthalmic (of-THAL-mik): Pertaining to the eye.

ophthalmologist (ŏf-thăl-MŎL-ō-jĭst): Specialist of the eye.

ophthalmology (Ophth) (ŏf-thăl-MŎL-ō-jē): Study of the eye.

ophthalmopathy (ŏf-thăl-MŎP-ă-thē): Disease of the eye.

ophthalmoplegia (of-thal-mō-PLĒ-j(ē-)ă): Paralysis of the eye.

ophthalmoscope (of-THAL-mŏ-skōp): Instrument used to view the eye.

ophthalmoscopy (of-thal-MOS-kŏ-pē): Process of viewing the eye.

opsonization (ŏp-să-nĭ-ZĀ-shŭn): An antibody or an antimicrobial protein binds to a pathogen, thereby marking it as a target for phagocytes.

optic (OP-tik): Pertaining to vision.

Optician (ŏp-TĬSH-ăn): Specialist who fills prescriptions for lenses but cannot prescribe.

Optometrist (ŏp-TŎM-ĕ-trĭst): Specialist who diagnoses, treats and manages diseases and disorders of the eye (Doctor of Optometry).

optometry (op-TOM-ĕ-trē): Measuring vision.

oral (ŌR-ăl): Pertaining to the mouth.

orchialgia (or-kē-ĂL-jē-ă): Pain in the testis.

orchiditis (or-kĭ-DĪ-tĭs): Inflammation of the testis.

orchiectomy (or-kē-EK-tŏ-mē): Excision of the testis.

orchiepididymitis (or-kē-ĕp-ĭ-dĭd-ĭ-MĪ-tĭs): Inflammation of the tested and epididymis.

orchiopexy (or-kē-ō-PĔK-sē): Surgical fixation of the testicle.

orchioplasty (OR-kē-ō-plăs-tē): Surgical repair of the testis.

orchiotomy (or-kē-ŎT-ō-mē): Incision into the testis.

orchitis (or-KĪ-tĭs): Inflammation of the testis.

organ (OR-găn): Anatomically distinct structure of the body composed of two or more tissue types.

organ system (OR-găn SIS-tĕm): Group of organs that work together to perform major functions or meet the physiological needs of the body.

organelle (OR-gă-nel): Tiny functioning units inside of a cell.

organism (OR-găn-ĭzm): Living being that has a cellular structure and can independently perform all physiological functions necessary for life.

orgasm (OR-gazm): A climax of sexual stimulation.

oropharynx (or-ō-FAR-ingks): The oropharynx is a passageway for both air and food and borders the nasopharynx and the oral cavity.

orthopnea (or-THŎP-nē-ă): Breathing is easier in a straight position.

osmosis (oz-MŌ-sĭs): A process by which molecules of a solvent tend to pass through a membrane from a less concentrated solution into a more concentrated one.

ostectomy (ŏs-TĔK-tō-mē): Excision of bone.

osteoarthritis (ä-stē-ō-är-ˈthrī-təs): Inflammation of bone and joint.

osteoblast (OS-tē-ō-blast): Developing bone cell.

osteochondritis (os-tē-ō-kon-DRĪT-ĭs): Inflammation of bone and cartilage.

osteoclasis (ŏs-tē-ō-KLĀ-sis): Surgical breaking of a bone.

osteocyte (OS-tē-ŏ-sīt): Bone cell.

osteomalacia (os-tē-ō-mă-LĀ-sh-ē-ă): Softening of the bones.

osteomyelitis (os-tē-ō-mī-ĕ-LĪT-ĭs): Inflammation of bone and bone marrow.

osteonecrosis (os-tē-ō-nĕ-KRŌ-sĭs): Abnormal condition of bone death (lack of blood supply).

osteopenia (os-tē-ō-PĒ-nē-ă): Abnormal reduction of bone mass.

osteopetrosis (ŏs-tē-ō-pĕ-TRŌ-sĭs): Abnormal condition of stone-like bones.

osteosarcoma (ŏs-tē-ō-săr-KŌ-mă): Malignant tumor of bone.

otalgia (ō-TĂL-jē-ă): Pain in the ear.

otologist (ō-TŎL-ō-jĭst): Specialist who studies and treats disorders and diseases of the ear.

otology (ō-TŎL-ō-jē): Study of the ear.

otomastoiditis (ō-tō-mas-toyd-ĪT-ĭs): Inflammation of the ear and mastoid bone.

otomycosis (ō-tō-mī-KŌ-sĭs): Abnormal condition of fungus in the ear.

otopyorrhea (ō-tō-pī-ō-RĒ-ă): Discharge of pus from the ear.

otorhinolaryngologist (ō-tō-RĪ-nō-lăr-ĭn-GŎL-ō-jĭst): Specialist or physician who studies and treats disease and disorder of the ears, nose and throat.

otorrhea (ō-tō-RĒ-ă): Discharge from the ear.

otosclerosis (ō-tō-sklē-RŌ-sĭs): Hardening of the ear.

otoscope (Ō-tō-skōp): Instrument used to view the ear.

otoscopy (ō-TŎS-kō-pē): Process of viewing the ear.

ovarian cancer (ō-VAR-ē-ăn KAN-sĕr): Malignant tumor of the ovary.

ovaries (Ō-vă-rēs): Two almond shaped organs (female gonads) located at the entrance to the fallopian tubes; responsible for storing of egg cells (ova) and production of estrogen and progesterone hormones.

ovulation (ov-yŭ-LĀ-shŏn): Release of ovum from a mature graafian follicle.

ovum (plural: ova) (Ō-vŭm): Female egg cells.

oximeter (ok-SIM-ĕt-ĕr): Instrument used to mesure oxygen.

oxytocia (ok-si-TŌ-sia): A rapid birth.