Sharp or biting in temper, mood, or tone.

*Acerbic* often describes wit. An acerbic critic won't make many friends among the writers or artists whose work is being criticized, but often keeps his or her readers amused and entertained. *Acerbity* may be slightly less sharp than sarcasm, but not much; both words have roots meaning basically “cut.”

Unpleasantly sharp and harsh; bitter.

*Acrid* exactly fits the smoke from a fire—a burning building or forest, for example. Dense smog may cast an acrid pall over a city, making throats burn and eyes sting. But, like *acid* and *acerbic*, *acrid* sometimes also describes nonphysical things, such as the remarks of a bitter person.

Harsh or bitter sharpness in words, manner, or temper.

Acrimony is angry harshness that usually springs from intense personal dislike. An *acrimonious* exchange is full of cutting, unpleasant remarks designed to hurt. Civil wars are often more acrimonious and bloody than foreign wars. In the same way, a bad divorce may be more acrimonious than any other kind of legal battle.

To make worse, more violent, or more severe.

To exacerbate is not to cause, but only to make something bad even worse. So the loss of a major industry in a city may exacerbate its already serious unemployment problem. A vicious remark can exacerbate a quarrel. Building a new mall may exacerbate an area's existing traffic problems. A new drug can exacerbate the side effects of the drug a patient is already taking. It used to be thought that too much blood in the body exacerbated a fever, so the patient's blood would be drained, often by means of leeches—and not all patients survived.

(1) A law or rule that limits or controls something; restriction. (2) A strong criticism.

*Stricture* has meant many things through the centuries, and its “restriction” meaning—probably the most common one today—is actually the most recent. High-school teachers often put strictures on texting during class. Cities concerned about their murder rate have slapped strictures on the possession of handguns. And the United Nations may vote to put strictures on arms sales to a country that keeps violating international treaties. With the meaning “strong criticism,” *stricture* is slightly old-fashioned today, but it's still used by intellectuals. So, for example, an article may amount to a harsh stricture on the whole medical profession, or an art review may just express the critic's strictures on sentimental paintings of cute little houses with glowing windows.

(1) Serving or likely to keep within bounds. (2) Serving or tending to place under limits as to use.

Restrictive covenants (that is, agreements) in real-estate deeds were once used to forbid the buyer from ever selling the property to anyone of another race. These are now illegal, though other kinds of restrictive covenants are very common; in some neighborhoods, they may even tell you what colors you can't paint your house. In grammar, a restrictive clause is one that limits the meaning of something that comes before it. In the sentence “That's the professor who I'm trying to avoid,” “who I'm trying to avoid” is a restrictive clause, since it's what identifies the professor. But in the sentence “That's my History professor, who I'm trying to avoid,” the same clause is *nonrestrictive*, since the professor has already been identified as “my History professor.” There should always be a comma before a nonrestrictive clause, but not before a restrictive clause.

(1) To draw together or make narrow. (2) To limit.

Arteries constricted by cholesterol slow the flow of blood, just as traffic arteries or highways constricted by accidents slow the flow of traffic. But *constriction* isn't always physical. Economic growth may be constricted by trade barriers. A narrow, constricted life may be the result of poverty or lack of opportunity. And an actress may feel constricted by a role she played as a child or by her TV character from years ago, which the public refuses to forget.

Something such as a nerve fiber or a drug that narrows a blood vessel.

Our blood vessels are constantly narrowing and widening in response to our activity or our environment, constricting in order to retain body heat and widening to get rid of excess heat. So when we're hot our skin flushes, and when we're very cold we become pale. Since the width of the blood vessels affects blood pressure, vasoconstrictors are prescribed to treat low blood pressure. Vasoconstrictors include antihistamines and amphetamines, as well as nicotine and caffeine; we commonly buy them for our runny noses and bloodshot eyes as well. The opposite of vasoconstrictors are *vasodilators*, which are commonly used to treat high blood pressure.