< V > TOEFL Vocabulary (152)

Optical (adjective)

of, relating to, or being objects that emit light in the visible range of frequencies  In 1936, Einstein calculated that an observer on Earth, given the correct line of sight,

might see multiple images of a single, distant object—a cosmic optical illusion, so to

speak. 

Optimism (noun) 

a tendency to expect a favorable outcome or to dwell on hopeful aspects

An atmosphere of optimism and a promise of prosperity among the settlers of

Chattanooga caused the city to prosper from 2,000 in 1865 to 12,000 in 1877.

Optional (adjective) 

not imposed on one by authority

It is learned that the writing process has a minimum of four stages and that there is an

optional fifth stage of writing. 

Oratorical (adjective) 

of or relating to the art of public speaking

As the boycott continued during 1956, King gained national prominence as a result of his

exceptional oratorical skills and personal courage. 

Orbit (adjective) 

of or relating to a course, process, or journey that ends where it began or repeats itself

19th century astronomers made very careful observations of Mercury's orbital

parameters but could not adequately explain those using Newtonian mechanics. 

Organism (noun) 

something resembling a living thing in its complexity of 

structure or functions

Researchers have learned that many different organisms can be conditioned to respond

to practically any stimuli such as lights, sounds, or tastes.

Originate (verb) 

to have as one’s home, place, or origin

Sulfates, which originate primarily in coal fired power plants, started rising around

1900.

Ornament (noun) 

the act of furnishing with decorations

Even department stores in some non-Christian countries are decorated with ornaments

during the Christmas season.

Oscillate (verb) 

to move back and forth with a steady rhythm

There is a special critical initial strength such that the field cannot decide whether to

evaporate away or collapse to form a black hole. Instead it oscillates increasingly

rapidly, performing an infinite number of oscillations in a finite time. 

Osmotic (adjective) 

relating to the diffusion through a semi-permeable membrane typically separating a 

solvent and a solution that tends to equalize their concentrations

Since saltwater fishes have blood with a lower concentration of salts than the

surrounding seawater, osmotic pressure tends to force water out of the body fluids and

to raise the internal salt concentration.