oblong leaf

a simple leaf that is rounded at each end with parallel sides ;

oblong woodsia

a common rock-inhabiting fern of northern temperate regions having rusty-brown stipes and lanceolate pinnate fronds ;

oblongness

the property of being shaped like a rectangle ;

obloquy

a false accusation of an offense or a malicious misrepresentation of someone's words or actions ; state of disgrace resulting from public abuse ;

obnoxiousness

the quality of being hateful ;

oboe

a slender double-reed instrument; a woodwind with a conical bore and a double-reed mouthpiece ;

oboe d'amore

a oboe pitched a minor third lower than the ordinary oboe; used to perform baroque music ;

oboe da caccia

an alto oboe; precursor of the English horn ;

oboist

a musician who plays the oboe ;

obolus

a Greek unit of weight equal to one tenth of a gram ;

obovate leaf

an egg-shaped leaf with the narrower end at the base ;

obscenity

an obscene act ; the trait of behaving in an obscene manner ; an offensive or indecent word or phrase ;

obscurantism

a deliberate act intended to make something obscure ; a policy of opposition to enlightenment or the spread of knowledge ;

obscurantist

a person who is deliberately vague ;

obscureness

the quality of being unclear or abstruse and hard to understand ; the state of being indistinct or indefinite for lack of adequate illumination ; the state of being humble and unimportant ;

obscurity

the quality of being unclear or abstruse and hard to understand ; the state of being indistinct or indefinite for lack of adequate illumination ; an obscure and unimportant standing; not well known; "he worked in obscurity for many years" ;

obsequiousness

abject or cringing submissiveness ;

observance

the act of observing; taking a patient look ; conformity with law or custom or practice etc. ; the act of noticing or paying attention; "he escaped the notice of the police" ; a formal event performed on a special occasion; "a ceremony commemorating Pearl Harbor" ;

observation

the act of observing; taking a patient look ; the act of making and recording a measurement ; the act of noticing or paying attention; "he escaped the notice of the police" ; facts learned by observing; "he reported his observations to the mayor" ; a remark expressing careful consideration ;

observation dome

lookout consisting of a dome-shaped observatory ;

observation post

an elevated post affording a wide view ;

observation station

a station set up for making observations of something ;

observation tower

a structure commanding a wide view of its surroundings ;

observatory

a structure commanding a wide view of its surroundings ; a building designed and equipped to observe astronomical phenomena ;

observed fire

fire for which the point of impact (the burst) can be seen by an observer; fire can be adjusted on the basis of the observations ;

observer

a person who becomes aware (of things or events) through the senses ; an expert who observes and comments on something ;

observer's meridian

a meridian that passes through the observer's zenith ;

obsession

an unhealthy and compulsive preoccupation with something or someone ; an irrational motive for performing trivial or repetitive actions against your will ;

obsessive

a person who has obsessions ;

obsessive-compulsive

a person with obsessive-compulsive characteristics ;

obsessive-compulsive disorder

an anxiety disorder characterized by recurrent and persistent thoughts and feelings and repetitive, ritualized behaviors ;

obsessive-compulsive personality

personality characterized by a strong need to repeat certain acts or rituals ;

obsessiveness

extreme compulsiveness ;

obsessivity

extreme compulsiveness ;

obsidian

acid or granitic glass formed by the rapid cooling of lava without crystallization; usually dark, but transparent in thin pieces ;

obsolescence

the process of becoming obsolete; falling into disuse or becoming out of date; "a policy of planned obsolescence" ;

obsoleteness

the property of being out of date and not current ;

obstacle

an obstruction that stands in the way (and must be removed or surmounted or circumvented) ; something immaterial that stands in the way and must be circumvented or surmounted; "lack of imagination is an obstacle to one's advancement"; "the poverty of a district is an obstacle to good education"; "the filibuster was a major obstruction to the success of their plan" ;

obstacle race

a race in which competitors must negotiate obstacles ;

obstetrical delivery

the act of delivering a child ;