Mathematical Bold Small Eta

The formula assigns its meaning; bold keeps it distinct from plain eta.

In many mathematical styles, bold lowercase letters mark vectors, especially in physics and applied math, but 𝛈 has no fixed meaning by itself. The formula and the author's definitions decide what it denotes. In LaTeX math, \boldsymbol{\eta} requests bold Greek eta; it formats a math expression rather than inserting this exact Unicode character.

The Greek letter behind it has a long path: Phoenician ḥet was borrowed as early Greek heta, Η. Some Greek dialects used Η for the h sound; Ionic speakers who had lost that sound reused it for a long e vowel. A mid-seventh-century BCE inscription from the Greek island of Naxos shows both uses. The Ionic vowel use became standard eta, while the western consonant branch led to Latin H.

Why does bold eta become regular eta?

Compatibility normalization can remove the bold distinction.

NFKC and NFKD are text-normalization steps that fold mathematical alphabets back to plain Greek or Latin letters. If 𝛈 and η name different quantities, either step makes them indistinguishable; preserve the unnormalized math text when the distinction matters.