Yet another excuse to write about the history of mathematics!

What Is Trigonometry?

http://www.livescience.com/51026-what-is-trigonometry.html

My editor left out the etymology of "sine" so I reproduce it here. From A History of Mathematics (3rd Edition) by Victor J. Katz (Section 8.7).

The English word ‘sine’ comes from a series of mistranslations of the Sanskrit ‘jyā-ardha’ meaning ‘chord-half.’ Aryabhata frequently abbreviated this term to ‘jyā’ or its synonym ‘jīvā.’ When some of the Hindu works were later translated into Arabic, the word was simply transcribed phonetically into an otherwise meaningless Arabic word ‘jiba.’ But since Arabic is written without vowels, later writers interpreted the consonants ‘jb’ as ‘jaib,’ which means bosom or breast. In the twelfth century, when an Arabic trigonometry work was translated into Latin, the translator used the equivalent Latin word ‘sinus,’ which also meant bosom, and by extension, fold (as in a toga over a breast), or a bay or gulf. This Latin word has now become our English ‘sine.’

That Malisha Dewalt over at MedievalPOC thought this was worth sharing tells me I'm doing something right in my representation of the history of math. I am happy.