A shrewdness of apes, a murder of crows, an unkindness of ravens and a crash of rhinos.

A new dictionary lists these little-known collective nouns, and explains the Schwartzchild radius, seven-league boots and the witch of Agnesi."The Dent Dictionary of Measurement" by publishing consultants Mike Darton and John Clark collects thousands of terms for quantification and measurement.

"As far as we know, no book with so many measurements has appeared before, and we hope it's interesting enough to read and not just refer to," Darton said in an interview.

Just published in the United States by Macmillan, the 538-page book has 3,500 entries.

It explains that "unkindness" as the term for a gathering of ravens arose in the Middle Ages when the big black birds were seen as portents of plague and death. It also reflects the old meaning of "unkind" as "unnatural."

The expression, the "shrewdness of apes" is of unknown origin, first used in 1452 as a term for a company of apes.

In the phrase "murder of crows," murder refers to noise as in the old expression.

And what about the crash of rhinos? They're nervous creatures, liable to panic and in charging they crash into trees and scrub.

Chemistry, math and physics account for most of the entries, but literary terms appear too.

"Grapheme" is the smallest unit of written language: generally a single letter for a vowel or consonant, sometimes a combination such as "th" or "ch."

The editors turn up some very odd measures on their way from "ab-" - a prefix used in theoretical electromagnetism - to "zymometry," the measuring of fermentation, usually in brewing.

"Gowpen" is the amount of water you can hold by cupping your hands.

Darton believes the oldest measurement in the book is "parasanges," also known as "parasang" and "farsang," a linear measure of about four miles used 4,000 years ago in Babylon.

His favorite measure is the "gry" because it was never actually put to use and is very, very small. Equivalent to 120th of an inch, it comes from a Greek word for a speck of dirt under a fingernail.

"I discovered it by chance when I was looking for something else in the Oxford English Dictionary," Darton said.

"Gry was a linear measure proposed for use in England in 1813 as part of a plan to make all linear measurements decimal-based. None of the other suggested units was adopted, and the gry is only remembered because it was smaller than any unit existing at the time," Darton said.

And how about the Schwartz-child radius?

American astrophysicist Martin Schwartzchild gave his name to the radius at which the gravitational forces of a collapsing star increase to the point that not even light can escape.

"It has become a black hole. For our sun, that critical radius is calculated to be about 1.86 miles," the dictionary says.

The witch of Agnesi is a "peculiar name for a fairly ordinary mathematical curve," named after Maria Gaetana Agnesi, an Italian mathematician.

Darton confessed to especially liking the tongue-in-cheek entries like "seven-league boots," magic footwear that enabled the wearer to travel seven leagues - about 21 miles - at each step.

"A wearer must remember to take the boots off before going indoors," Darton added to the entry.