Pongal: history of word and entity?

[Geeta Bharathan]

This question came up during a food-related discussion (on the northern
khichri vs. southern Pongal).

The point of contention is whether pongal and khichri are equivalent; I
say not: pongal, either as word nor entity, is not the 'hodge-podge'
suggested by 'khichri'. I went out on a limb to suggest that pongal, at
least in the Tamil context, also occupies a different culinary/cultural
niche related to its association with the harvest festival (coming up
next week, and very hard to visualize when surrounded by snow).

Now I come to this group to ask: is this even remotely true? what do we
know about the history of the word 'pongal' (in Tamil and in other
southern languages) and its association with the festival (in Tamil nadu,
but not in other parts of southern India?)?

Thanks for any insights!

--Geeta