Iota Symbol (ι): Meaning, Uses and How to Type It

Iota is the ninth letter of the Greek alphabet and its smallest: the lowercase ι is a single short stroke with no dot. That smallness gave English the phrase "not one iota," and it made the letter a natural name for tiny or elementary things in mathematics and programming, from the inclusion map ι to the APL index generator ⍳ and the iota keywords of C++ and Go.

This guide explains what iota means and how to type ι and Ι on any device, in HTML and in LaTeX.

Iota Definition

Iota (noun): 1. the ninth letter of the Greek alphabet, written Ι (capital) and ι (small), pronounced "eye-OH-tuh" in English and "YO-ta" in modern Greek. It comes after theta (θ) and before kappa (κ), stood for 10 in the Greek numeral system, and is the ancestor of the Latin letters I and J. 2. A very small amount, as in "there is not an iota of truth in it."

The second meaning comes from the letter's size. In the King James Bible, Matthew 5:18 promises that "one jot or one tittle" of the law will not pass away; "jot" is the English form of iota, the smallest letter of the Greek original. For all 24 letters with their LaTeX commands, see the Greek alphabet in LaTeX lesson, and for how each letter is used as a math symbol, see Greek letters as math symbols.

Iota Symbol (ι): Copy and Paste

Copy the letters from the box below (use the copy button), or take the code you need from the table:

1ι Ι ℩ ⍳
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The box also contains two related symbols: the turned iota ℩ (U+2129) used in logic, and the APL iota ⍳ (U+2373). LaTeX has no \Iota command because uppercase iota is identical to a Latin I; write I or \mathrm{I}.

What the Iota Symbol Means

Iota is rare in science, because ι is easy to mistake for a dotless i or the number 1. Where it appears, it marks something small or structural.

Inclusion Maps in Mathematics

In algebra, topology and category theory, ι (or i) is the conventional name for an inclusion or canonical injection, the map that sends each element of a subset to itself inside a larger set:

ι : A → B, ι(a) = a for every a in A ⊆ B

For example, the inclusion of the integers into the rationals is ι : ℤ → ℚ, and the maps into a coproduct are often called ι₁ and ι₂.

The Turned Iota in Logic

In Principia Mathematica (1910), Whitehead and Russell wrote the definite description "the unique x such that φ(x)" with an upside-down iota: ℩x φ(x). The notation, still used in philosophy of language and formal logic, is why Unicode includes the separate character ℩ (TURNED GREEK SMALL LETTER IOTA, U+2129).

Iota in Programming

Programmers borrowed the letter for counting from the start. In APL, the iota function ⍳ is the index generator: ⍳5 returns 1 2 3 4 5. C++ took the name for std::iota in the <numeric> header (since C++11), which fills a range with successive values, and Go uses iota inside a const block as a counter that starts at 0 and increases by one on each line:

1const (
2    Sunday = iota // 0
3    Monday        // 1
4    Tuesday       // 2
5)
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How to Type Iota

Windows: iota has no short Alt code in the old IBM character set. In Word, type 03B9 and press Alt + X; elsewhere, open Character Map and search "iota."

Mac: there is no Option-key shortcut. Add the Greek input source in System Settings > Keyboard > Input Sources and press I for ι or Shift + I for Ι, or open the Character Viewer with Control + Command + Space and search "iota."

iPhone and Android: add the Greek keyboard (Settings > General > Keyboard > Keyboards on iOS, or Gboard's language settings), switch with the globe key and tap I.

Microsoft Word: type 03B9 and press Alt + X (0399 for Ι), or use Insert > Symbol > More Symbols with the Greek and Coptic subset. Inside a Word equation (Alt + =), \iota followed by a space also works.

Google Docs: go to Insert > Special characters and search "iota," or open Insert > Equation and type \iota followed by a space.

HTML: write ι for ι and Ι for Ι, or the numeric forms ι and Ι.

Iota in LaTeX

Use \iota in math mode. Because uppercase iota looks exactly like a Latin I, standard LaTeX has no \Iota; write I or \mathrm{I}. Do not confuse \iota with \imath, which gives a dotless i (ı) for placing accents over an i.

A complete example you can compile:

1\documentclass{article}
2\usepackage{amsmath,amssymb}
3\begin{document}
4The inclusion $\iota \colon \mathbb{Z} \hookrightarrow \mathbb{Q}$ sends $n$ to $n/1$.
5\[
6  \iota_1 \colon A \to A \sqcup B, \qquad \iota_2 \colon B \to A \sqcup B
7\]
8A dotless i for accents is $\hat{\imath}$, which is not an iota.
9\end{document}
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Related symbols and guides

• Iota symbol page — copy the symbol and its LaTeX command
• Greek letters reference — every symbol in the category with its LaTeX command
• Greek alphabet in LaTeX — how to typeset these symbols in a document
• Eta symbol (η)
• Kappa symbol (κ)

Iota Symbol FAQ

What is the iota symbol?

The iota symbol is the Greek letter iota: ι in lowercase (U+03B9) and Ι in uppercase (U+0399). It is the ninth letter of the Greek alphabet, and as a symbol it names inclusion maps in mathematics, while the related characters ℩ and ⍳ are used in logic and APL.

What does "not one iota" mean?

It means "not even the smallest amount." Iota is the smallest letter of the Greek alphabet, so it came to stand for a tiny quantity, and the English word "jot" comes from the same letter.

How do you type the iota symbol?

In Word type 03B9 and press Alt + X. On a Mac or phone, add the Greek keyboard and press I. In HTML write ι, and in LaTeX write \iota. Or copy ι from the box at the top of this page.

Is ι the same as a dotless i?

No. The Greek iota ι (U+03B9) and the dotless i ı (U+0131) used in Turkish are different characters with different code points. In LaTeX, \iota gives the Greek letter and \imath gives a dotless i for use under accents.

What does iota mean in programming?

In APL, ⍳ generates the list of integers 1 to n. In C++, std::iota fills a range with increasing values starting from a given number. In Go, iota is a counter that numbers the constants in a const block, starting at 0.

Writing with Greek Symbols

Inclusion maps, logic notation and code listings all need the right character: a true Greek ι in equations, typeset consistently and never swapped for an i or a 1. Octree is an AI-powered LaTeX editor that turns plain-language descriptions into properly formatted equations. Create professional documents at useoctree.com.