billion

the word 'billion' entered english from french in the late 17th century. it was originally formed within french from 'bi-' (meaning 'two') and '-illion', a suffix modeled on 'million'. the core logic was that a billion was a "second power of a million" (i.e., a million millions, or 1,000,000^2). this created the long-scale system where 'billion' meant a trillion (1,000,000,000,000) in historical british usage. however, in the 20th century, american english adopted the short-scale system where each new '-illion' term represents a thousand times the previous one, making a billion equal to a thousand millions (1,000,000,000). this short-scale definition has now become standard in most english-speaking regions and international scientific contexts, fundamentally shifting the word's numerical value while retaining its sense of an immense quantity.

the word is a simplex loanword from french, built on the root 'bi-' (two) and the augmentative suffix '-illion'. it is not productively segmented in modern english spelling.