■ The ratio of the circumference of a circle to its diameter (pi).
□ The curious thing about this term is that there is no corresponding English word, except "pi" (π), the name of the symbol for its value (which comes from the first letter of the Greek periphereia). This may be why there is no entry for 円周率 in the Japanese edition of the McGraw-Hill Dictionary of Scientific and Technical Terms, because the dictionary was translated from English.
◇ Just for reference, the first few decimal places of the value of pi are as follows:
3.1415926535 8979323846 2643383279 5028841971 6939937510 5820974944...
This entry was created by Brian Chandler.