(1) A formal command. (2) Permission to act, given by the people to their representatives.

A mandate from a leader is a command you can't refuse. But that kind of personal command is rarely the meaning of *mandate* today; much more common are connected with institutions. Thus, the Clean Air Act was a mandate from Congress to clean up air pollution—and since *mandate* is also a verb, we could say instead that the Clear Air Act *mandated* new restrictions on air pollution. Elections are often interpreted as mandates from the public for certain kinds of action. But since a politician is not just a symbol of certain policies but also an individual who might happen to have an awfully nice smile, it can be risky to interpret most elections as mandating anything at all.

Required.

Something mandatory is the result of a *mandate* or order, which usually comes in the form of a law, rule, or regulation. Today there seem to be a lot of these mandates, so mandatory seat belts, mandatory inspections for industries, and mandatory prison sentences for violent crimes are regularly in the news. But mandatory retirement at age 65, which used to be common, is now illegal in most cases.

To take possession of something by force, especially for military purposes.

Military forces have always had the power to commandeer houses. The Declaration of Independence complains about the way the British soldiers have done it, and the third Amendment to the Constitution states that the commandeering of people's houses shall be done only in a way prescribed by law. Almost anything—food, supplies, livestock, etc.—can be militarily commandeered when the need arises. But you don't have to be in the military for someone to “pull rank” on you: Your father may commandeer the car just when you were about to take it out for the evening, your teacher may commandeer your cell phone as you're texting in the middle of class, or your older sister may commandeer the TV remote to watch some lousy dancing competition.

(1) To order a case sent back to another court or agency for further action. (2) To send a prisoner back into custody to await further trial or sentencing.

*Remand* means “order back” or “send back.” After losing a case in a lower court, lawyers will frequently appeal it to a higher court. If the higher court looks at the case and sees that the lower court made certain kinds of errors, it will simply remand it, while telling the lower court how it fell short the first time: by not instructing the jury thoroughly, for example, or by not taking into account a recent related court decision.

(1) Rising and falling in waves. (2) Wavy in form, outline, or surface.

The surface of a freshly plowed field is undulant. A range of rolling hills could be called undulant, as could the shifting sands of the Sahara. A waterbed mattress is often literally undulant. And a field of wheat will *undulate* or sway in the wind, like the waves of the sea.

(1) To cover with a flood or overflow. (2) To overwhelm.

In the summer of 1993, record rains in the Midwest caused the Mississippi River to overflow its banks, break through levees, and inundate the entire countryside; such an *inundation* hadn't been seen for at least a hundred years. By contrast, the Nile River inundated its entire valley every year, bringing the rich black silt that made the valley one of the most fertile places on earth. (The inundations ceased with the completion of the Aswan High Dam in 1970.) Whenever a critical issue is being debated, the White House and Congressional offices are inundated with phone calls and e-mails, just as a town may be inundated with complaints when it starts charging a fee for garbage pickup.

(1) To have an effect for good or bad. (2) To rebound or reflect.

*Redound* has had a confusing history. Its original meaning was simply “overflow.” But since the prefix *re-* often means “back,” the later meaning “result” may have arisen because flowing back—on a beach, for example—is a result of the original flowing. *Redound* has long been confused with other words such as *resound* and *rebound,* so today “rebound” is another of its standard meanings. As examples of its usual meaning, we could say that the prohibition of alcohol in 1919 redounded unintentionally to the benefit of gangsters such as Al Capone—and that Capone's jailing on tax-evasion charges redounded to the credit of the famous “Untouchables.”

(1) The state of being extra or unnecessary. (2) Needless repetition.

*Redundancy*, closely related to *redound*, has stayed close to the original meaning of “overflow” or “more than necessary.” Avoiding redundancy is one of the prime rules of good writing. ““In the modern world of today” contains a redundancy; so does “He died of fatal wounds” and “For the mutual benefit of both parties.” But redundancy doesn't just occur in language. “Data redundancy” means keeping the same computer data in more than one place as a safety measure, and a backup system in an airplane may provide redundancy, again for the sake of safety.