From Gurunet:

tur·mer·ic (tûr'mər-ĭk, tū'-)
n.
1. A widely cultivated tropical plant (Curcuma domestica) of India, having yellow flowers and an aromatic, somewhat fleshy rhizome.
2. The powdered rhizome of this plant, used as a condiment and a yellow dye.
3. Any of several other plants having similar rhizomes.

[Alteration of Middle English termeryte, from Old French terre-merite, saffron, from Medieval Latin terra merita : Latin terra, earth + Latin merita, feminine past participle of merēre, to deserve.]

Wonder if that merit part has anything to do with why it's used for the dot.

Edit: woops! Sorry for mantling you, Father Steve; I should have gone to your link before making my post. Your link was better, in any case.