SIGMA

Meaning

The eighteenth letter of the Classical and Modern Greek alphabets, the twentieth letter of Old and Ancient.

SIGMA as a word-puzzle answer

SIGMA is a 5-letter word with 2 vowels (I, A) and 3 consonants (S, G, M). Every letter is distinct, so it rarely punishes a clean opening guess.

It leans on high-frequency letters (S, I, A), so a strong vowel-and-common-consonant opener tends to light up quickly. There are no rare letters here, so it is a fair, mid-difficulty answer for the daily Classic puzzle.