Hypertext Webster Gateway: "Subindex"
From Webster's Revised Unabridged Dictionary (1913) (web1913)
Subindex \Sub*in"dex\, n.; pl. {Subindices}. (Math.)
A number or mark placed opposite the lower part of a letter
or symbol to distinguish the symbol; thus, a_{0}, b_{1},
c_{2}, x_{n}, have 0, 1, 2, and n as subindices.
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