# Is there a technical term for a 'complementing' number that sums to 1?

I'm looking for a technical name (if one exists) for a number that 'completes' or 'complements' another. The motivation for this is to develop a proper understanding of mathematical language, for example in naming variables while programming.

Say if I have a value x = 1/26. Is there a name for y = 25/26 that fills in the remaining part of the fraction?

In essence, if I have some x, I want a technical name for the value of y = (1-x).

• difference maybe? – JHance Aug 13 '14 at 17:23

• If $x$ were the probability of an event then $1-x$ would be the probability of the complementary event, not the complementary event itself. I'm not convinced a widespread snappy name for $1-x$ (in terms of $x$) exists, especially not outside of probability theory. – Clive Newstead Aug 13 '14 at 17:27