Obstetrics – study of midwifery Oceanography – study of oceans Oceanology – study of oceans Odontology – study of teeth Odonatology– study of dragonflies and damselfies Oenology – study of wines Oikology – science of housekeeping Olfactology – study of the sense of smell Ombrology – study of rain Oncology – study of tumours Oneirology – study of dreams Onomasiology – study of nomenclature Onomastics – study of proper names Ontology – science of pure being; the nature of things Oology – study of eggs Ophiology – study of snakes Ophthalmology – study of eye diseases Optics – study of light Optology – study of sight Optometry – science of examining the eyes Orchidology – study of orchids Ornithology – study of birds Orology – study of mountains Orthoepy – study of correct pronunciation Orthography – study of spelling Orthopterology – study of cockroaches Oryctology – mineralogy or paleontology Osmics – scientific study of smells Osmology – study of smells and olfactory processes Osphresiology – study of the sense of smell Osteology – study of bones Otology – study of the ear Otorhinolaryngology – study of ear, nose and throat