Don't know about a
Kośa reference, but the word clearly betrays a Dravidian connection. See
[DEDR 4796] and [
CDIAL 9996].
Burrow discusses this word in "Dravidian Studies VII", Bulletin of the School of Oriental and African Studies, University of London, Vol. 12,No. 2 (1948), pp. 365-396 (See entries 259 and 275).
275. meṭa- m. a whitewashed, storied house, L. [Pkt. meḍaya-; Guj. meḍī, meḍo an upper storey, etc.].
~ Te. mēḍa a house of two or more stories, Ta. mēṭai raised floor, platform, terraced house. Cf. māḍi.
Regards,
Suresh.