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Related to razor: Razor burn
(as) sharp as a razor
1. Literally, having an extremely sharp point or edge. Be careful picking up those shards of broken glass! They're as sharp as razors. No one but Mommy or Daddy is allowed to use this carving knife, OK Tommy? It's sharp as a razor, and could take your whole finger off if you're not careful!
2. Very intelligent, witty, and quick-thinking. My grandmother's became very physically incapacitated as she grew older, but her mind was as sharp as a razor until the day she died. Of course Ellen is our valedictorian—she's sharp as a razor!
dance on the razor's edge
To do something risky or dangerous. Please, you just like him because he's the bad boy who dances on the razor's edge with his motorcycle! I like to dance on the razor's edge sometimes and do things like skydive and bungee jump.
A maxim that the simplest theory should be applied to a situation or experiment first. This concept is named for its ardent defender, 14th-century philosopher William of Occam. I think our initial hypothesis is too complex. Occam's razor would suggest we consider the simplest possible explanation.
on a razor's edge
With the possibility of failing or changing drastically very suddenly or at any given moment. The stability of the market is on a razor's edge, as banks struggle to deal with a huge number of failing mortgages and bad debts. The policy norms for the country tend to be on a razor's edge, as the majority in congress constantly shifts between the two major political parties.
on the razor's edge
To the point of doing something risky or dangerous. Please, you just like him because he's the bad boy who dances on the razor's edge with his motorcycle. I like to live on the razor's edge sometimes and go skydiving.
1. Literally, very sharp, like a razor. Stand back, that tool is razor-sharp! Please be careful cutting those vegetables with such a razor-sharp knife.
2. Particularly clear, perceptive, and/or intelligent. Victoria may seem quiet, but she always has these razor-sharp insights on the texts we're reading. The think tank is known for razor-sharp analysis of world affairs. A lot of people are funny, but she has razor-sharp wit.
sharp as a razor
1. very sharp. (*Also: as ~.) The penknife is sharp as a razor. The carving knife will have to be as sharp as a razor to cut through this gristle.
2. and sharp as a tack very sharp-witted or intelligent. (*Also: as ~.) The old man's senile, but his wife is as sharp as a razor. Sue configure things out from even the slightest hint. She's as sharp as a tack.
sharp as a tack
Also, sharp as a razor. Mentally acute. For example, She's very witty-she's sharp as a tack. These similes are also used literally to mean "having a keen cutting edge" and have largely replaced the earlier sharp as a needle or thorn. The first dates from about 1900, the variant from the mid-1800s.
on a razor's edge
If a situation is on a razor's edge it could change or be decided at any time, often in a way that is dangerous. I knew my life at that moment hung on a razor's edge. In this election Ohio is balanced on a razor's edge between Republicans and Democrats.
Occam's razorthe principle that in explaining something no more assumptions should be made than are necessary.
This principle takes its name from the English philosopher and Franciscan friar William of Occam ( c .1285–1349 ): the image is that of the razor cutting away all extraneous assumptions.
(as) sharp as a ˈtack(American English) intelligent with a quick and lively mind: My grandmother’s 85 but she’s still sharp as tack.
A tack is a kind of small nail or pin.
The simplest explanation of something is apt to be the correct one. This principle is named for the English scholar William of Occam (or Ockham), who lived from 1280 to 1349. A Franciscan monk, he so angered Pope John XXII through both his writings on the nature of knowledge and his defense of his order’s vow of poverty that he was excommunicated. William, whom his colleagues called Doctor Singularis et Invincibilis (“singular and invincible doctor”), put his principle in Latin: Entia non sunt multiplicanda praeter necessitatem, “Entities should not be unnecessarily multiplied.” In effect, he held that any unnecessary parts of a subject being analyzed should be eliminated. Obviously, this could simply be called Occam’s Principle, and indeed, the razor did not enter into it until a French philosopher, Etienne Bonnot de Condillac, in 1746 called it Rasoir des Nominaux, “the razor of the nominalists,” that is, cutting through complicated arguments to reach the truth. In 1836 Sir William Hamilton, lecturing on metaphysics and logic, put the two ideas together, saying, “We are therefore entitled to apply Occam’s razor to this theory of causality.” While some may believe that this phrase, with its ancient and rather abstruse origin, is obsolete, novelist Archer Mayor clearly disagreed, for he entitled his 1999 murder mystery Occam’s Razor.
razor's edge, on the
In a critical or dangerous predicament. This analogy dates from Homer’s time (Iliad, ca. 850 b.c.): “To all it stands on a razor’s edge, either woeful ruin or life for the Achaeans.” W. Somerset Maugham used it as the title of a philosophical novel (The Razor’s Edge, 1944) exploring the meaning of life. Alan White used it in The Long Silence (1976): “He was living on a razor’s edge. Sooner or later, the Germans were going to begin to suspect.”
See also: on
sharp as a tack
Singularly keen or cutting; also, mentally acute. This simile has largely supplanted the earlier sharp as a razor, needle, vinegar, and thorn, the last dating from the fifteenth century and appearing in John Ray’s 1670 proverb collection. The current cliché dates from the late nineteenth or early twentieth century and appeared in a 1912 issue of Dialect Notes: “They won’t fool him; he’s sharp as tacks.”