What does tri in trillion mean?

Answer 1

The tri- refers to three.

The prefices come from the European use where the prefices represented the powers of a million. This is known as the long scale.

billion = million^2 (bi- = 2)

trillion = million^3 (tri- = three)

quadrillion = million^4 (quadra- = four)

and so on.

This meant that a number with a prefix representing the number n had 6n zeros.

However, most non-European countries, as well as the UK, use the short scale. In this scale, there is no direct link between the prefix and the power. From a billion onwards, (prefix + 1) is the power of 1000. In this scale, a number with a prefix representing the number m had 3*(m+1) zeros.

Answer 2

Three