There is no definite philological and linguistic basis for asserting unilaterally that the name Dravida also forms the origin of the word Tamil (Dravida -> Dramila -> Tamizha or Tamil). Zvelebil cites the forms such as dramila (in 's Sanskrit work Avanisundarīkathā) (found in Ceylonese chronical Mahavamsa) and then goes on to say (ibid. page xxi): "The forms /damila almost certainly provide a connection of " and "... < ...whereby the further development might have been * > * > - / damila- and further, with the intrusive, 'hypercorrect' (or perhaps analogical) -r-, into . The -m-/-v- alternation is a common enough phenomenon in Dravidian phonology" (Zvelebil 1990:xxi)
Further another eminent Dravidian linguist Bhadriraju Krishnamurti in his book Dravidian Languages (Krishnamurti 2003:p2, footnote 2) states: "Joseph (1989: IJDL 18.2:134-42) gives extensive references to the use of the term , dramila first as the name of a people, then of a country. Sinhala inscriptions cite -, damela- denoting Tamil merchants. Early Budhdhist and Jaina sources used - to refer to a people of in south India (presumably Tamil); - was a southern non-Aryan country; -, , and - were used as variants to designate a country in the south (Kādambarī, Daśakumāracarita-, fourth to seventh centuries AD) (1989: 134-8). It appears that - was older than - which could be its Sanskritization."
Based on what Krishnamurti states referring to a scholary paper published in the International Journal of Dravidian Linguistics the Sanskrit word itself is later than since the dates for the forms with -r- are centuries later than the dates for the forms without -r- (-, damela- etc.). So it is clear that it is difficult to maintain Dravida -> Dramila -> Tamizha or Tamil.
The Monier-Williams Sanskrit Dictionary lists for the Sanskrit word draviḍa a meaning of "collective Name for 5 peoples, viz. the Āndhras, Karṇāṭakas, Gurjaras, Tailaṅgas, and Mahārāṣṭras".
Consonants: Proto-Dravidian is reconstructible with the following consonantal phonemes (Subrahmanyam 1983:p40, Zvelebil 1990, Krishnamurthi 2003):
|Fricative||ḻ (ṛ, r̤)||(h)|
The alveolar stop *ṯ in many daughter languages developed into an alveolar trill /r/. The stop sound is retained in Kota and Toda (Subrahmanyam 1983). Malayalam still retains the original (alveolar) stop sound in gemination. (ibid). In Old Tamil it took the enunciative vowel like the other stops. In other words, *ṯ (or *ṟ) did not occur word-finally without the enunciative vowel (ibid).
Velar nasal *ṅ occurred only before *k in Proto-Dravidian (as in many of its daughter languages). Therefore it is not considered a separate phoneme in Proto-Dravidian. However, it attained phonemic status in languages like Malayalam, Gondi, Konda and Pengo due to the simplification of the original sequence *ṅk to *ṅ. (Subrahmanyam 1983)
The glottal fricative *h has been proposed by Bh. Krishnamurthi to account for the Old Tamil Aytam (Āytam) and other Dravidian comparative phonological phenomena (Krishnamurthi 2003).
However this is disputed and the Indus valley script is yet to be conclusively deciphered.
The identification of Indus Valley Civilization language with some form of Dravidian has not been conclusive or successful. Iravatham Mahadevan, who with his knowledge of both Tamil and Sanskrit, spent many decades studying the IVC script said in an interview in 1998 that IVC script is undeciphered. According to Michael Witzel, the well-known Indologist, there are not many Dravidian loan words in the earliest stratum of Vedas, even though, the Dravidian influence quickly increases in the post-Rigvedic period. In the essay "Substrate Languages in Old Indo-Aryan", Prof. Witzel says "As we can no longer reckon with Dravidian influence on the early RV, this means that the language of the pre-Rigvedic Indus civilization, at least in the Panjab, was of (Para-) Austro-Asiatic nature."