>Can someone please explain what Tamil aytham originally represented
>and now represents in Tamil?
As far as I know it represented /h/ in Old Tamil. In
Steever's Dravidian Languages, it is said (Proto-Dravidian
"The phoneme *h represented the predecessor of Old Tamil
a:ytam, conventionally transliterated as <k_>. Recent
proposals attempt to establish it as an independent phoneme
in the proto-language, but it seems to have been an
allophone of *y that appeared in the environment V_C."
The sign is called "Tamil visarga" in the Unicode standard,
which I suppose means that its origin is the visarga sign
/h./, used in Sanskrit for a voiceless /h/.
Miguel Carrasquer Vidal mcv@...