What does trillionth mean?
The word trillionth is the formal ordinal and fractional form of trillion. As a noun, it means one of a trillion equal parts; as an ordinal adjective, it identifies the trillionth member of a sequence. Its exact numerical value depends on the numbering convention: under the short scale, where a trillion is 10^12, a trillionth is 10^-12; in the traditional long scale, where a trillion is 10^18, it is 10^-18. It is especially useful in scientific and technical prose for expressing extremely small intervals, proportions, or degrees of precision, as in “a trillionth of a second.” In ordinary conversation, the term conveys the idea of a vanishingly small quantity, although its full form carries a precise mathematical implication. As an ordinal, trillionth emphasizes the enormity of a position or count rather than smallness. Modern British and American English generally use the short scale, although older British usage and some international contexts retain the long scale. The suffix -th follows the ordinary English pattern of forming ordinals from cardinal numbers.
Denoting the member or position that is number one trillion in a series.
"The trillionth request exhausted the counter and triggered the alert."
Used formally in mathematical, scientific, and technical contexts.
A part equal to one of a trillion equal parts of a whole.
"Under short-scale terminology, a nanosecond is one trillionth of a second."
The exact value is 10^-12 under the short scale and 10^-18 under the traditional long scale.
The plural is used when referring to multiple separate fractions of this size.
"At this precision, errors of several trillionths of a second become significant."
Under short-scale numbering, splitting one second into a trillion equal pieces gives you nanoseconds.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does trillionth come from?
The word was formed in English by adding the ordinal suffix -th to trillion. Trillion entered English in the 17th century from Italian trilione, which derives from Latin tres, meaning “three,” and milia, meaning “thousands.” The same Latin numerical root underlies related English words such as trinity, trilateral, and triangle.
Related word forms
How trillionth is actually used
This is primarily formal, mathematical, and scientific vocabulary. Its numerical value follows the scale convention used for trillion: under the short scale it means 10^-12, while under the traditional long scale it means 10^-18.
Easily confused with trillionth
A trillion is the large cardinal number itself, whereas a trillionth is one part in a trillion equal parts or the corresponding ordinal position.
A billionth is based on a billion, while a trillionth is based on a trillion; their numerical values and scale conventions therefore differ.