O

oakum n. Hemp-fiber obtained by untwisting and picking out loosely the yarns of old hemp rope.
obdurate adj. Impassive to feelings of humanity or pity.
obelisk n. A square shaft with pyramidal top, usually monumental or commemorative.
obituary adj. A published notice of a death.
obligate v. To hold to the fulfillment of duty.
obligatory adj. Binding in law or conscience.
oblique adj. Slanting; said of lines.
obsequies n. Funeral rites.
obsequious adj. Showing a servile readiness to fall in with the wishes or will of another.
obsolescence n. The condition or process of gradually falling into disuse.
obsolescent adj. Passing out of use, as a word.
obstetrician n. A practitioner of midwifery.
obstetrics n. The branch of medical science concerned with the treatment and care of women during pregnancy.
obstinacy n. Stubborn adherence to opinion, arising from conceit or the desire to have one's own way.
obstreperous adj. Boisterous.
obstruct v. To fill with impediments so as to prevent passage, either wholly or in part.
obstruction n. Hindrance.
obtrude v. To be pushed or to push oneself into undue prominence.
obtrusive adj. Tending to be pushed or to push oneself into undue prominence.
obvert v. To turn the front or principal side of (a thing) toward any person or object.
obviate v. To clear away or provide for, as an objection or difficulty.
Occident n. The countries lying west of Asia and the Turkish dominions.
occlude v. To absorb, as a gas by a metal.
octave n. A note at this interval above or below any other, considered in relation to that other.
octavo n. A book, or collection of paper in which the sheets are so folded as to make eight leaves.
octogenarian adj. A person of between eighty and ninety years.
oculist n. One versed or skilled in treating diseases of the eye.
ode n. The form of lyric poetry anciently intended to be sung.
odious adj. Hateful.
odium n. A feeling of extreme repugnance, or of dislike and disgust.
officiate v. To act as an officer or leader.
olfactory adj. of or pertaining to the sense of smell.
omnipotence n. Unlimited and universal power.
Omnipotent adj. Possessed of unlimited and universal power.
omniscient adj. Characterized by unlimited or infinite knowledge.
onerous adj. Burdensome or oppressive.
onrush n. Onset.
onus n. A burden or responsibility.
opalescence n. The property of combined refraction and reflection of light, resulting in smoky tints.
operetta n. A humorous play in dialogue and music, of more than one act.
opprobrium n. The state of being scornfully reproached or accused of evil.
optic n. Pertaining to the eye or vision.
optician n. One who makes or deals in optical instruments or eye-glasses.
optics n. The science that treats of light and vision, and all that is connected with sight.
optometry n. Measurement of the powers of vision.
opulence n. Affluence.
opulent adj. Wealthy.
orate v. To deliver an elaborate or formal public speech.
oration n. An elaborate or formal public speech.
oratorio n. A composition for solo voices, chorus, and orchestra, generally taken from the Scriptures.
oratory n. The art of public speaking.
ordinal n. That form of the numeral that shows the order of anything in a series, as first, second, third.
ordination n. A consecration to the ministry.
ordnance n. A general name for all kinds of weapons and their appliances used in war.
orthodox adj. Holding the commonly accepted faith.
orthodoxy n. Acceptance of the common faith.
orthogonal adj. Having or determined by right angles.
orthopedic adj. Relating to the correcting or preventing of deformity
orthopedist n. One who practices the correcting or preventing of deformity
oscillate v. To swing back and forth.
osculate v. To kiss.
ossify v. to convert into bone.
ostentation n. A display dictated by vanity and intended to invite applause or flattery.
oust v. To eject.
outrigger n. A part built or arranged to project beyond a natural outline for support.
overstride v. To step beyond.