written or printed below and to one side of another character
source: WordNet 3.0
Written below or underneath; as, iota subscript. (See under Iota.) Specifically (Math.), said of marks, figures, or letters (suffixes), written below and usually to the right of other letters to distinguish them; as, a, n, 2, in the symbols Xa, An, Y2. See Suffix, n., 2, and Subindex.
source: Webster 1913
noun
a character or symbol set or printed or written beneath or slightly below and to the side of another character
