radar¹ - n. a device² that uses radio signals to learn the position or speed of objects that may be too far away to be seen

radiation - n. waves of energy from something that produces heat or light; energy from a nuclear substance, which can be dangerous

radio - n. the system of sending and receiving signals or sounds through the air without wires

raid³ - v. to make a sudden attack; n. a sudden attack carried out as an act of war, or for the purpose of seizing or stealing something

railroad⁴ - n. a road for trains; a company that operates such a road and its stations and equipment

rain - n. water falling from the sky

raise - v. to lift up; to move to a higher position; to cause to grow; to increase

rare - ad. not common; not usual; not often

rate - n. speed; a measure of how quickly or how often something happens; the price of any thing or service that is bought or sold

reach - v. to put a hand toward⁵; to arrive at; to come to

react - v. to act as a result of or in answer to

read - v. to look at and understand the meaning of written words or numbers

ready - ad. prepared; completed; organized; willing

real - ad. true; truly existing; not false

realistic - ad. in agreement with the way things are

reason - n. the cause for a belief or act; purpose; something that explains

reasonable - ad. ready to listen to reasons or ideas; not extreme; ready or willing to compromise