(1) Tamil has three letters to represent N sound.
(2) It has three letters to represent L sound
(3) It has two letters to represent R sound.
(4) No word can start with a pure consonant. For example, the name “Krishnan” cannot be wriiten if one adheres to proper grammar. It is usually written as “Kirusnan” and generally pronounced as “Krishnan”. Pure grammar makes this word to be Kannan.
(4a) Tamil will avoid consonant clusters completely. For example a Sanskrit word like “Nakshathra” cannot be written. It is generally written by inserting vowels to squash / break the consonant clusters, like “Natsathiram” etc.
(5) It does not have aspirated consonants. It has only one consonant symbol to represent K, KH, G, Gh and H. The pronunciation is generally done depending on the place of the letter in the word and generally obeys an unwritten rule of “as per easy flow”. Generally sounds like Kh, Gh do not occur. Similarly there is only one representation in the place of 4 which other Indians are used for “S”, “T” and “P”.
(6) Some consonant sounds are prohibited to appear at the beginning of words. For example T cannot appear at the beginning of a word. If a word starts with a pure T , then it is not a Tamil word. Of the 18 consonants the following is the break up:
Allowed ones: Ka, Sa, Gna, Na, Tha, Pa, Ma, Ya, Va
Disallowed ones: nga, Ta, Nna, Nnna, la, lla, zha, ra, rra.
The letter Y can only start a word if it is accompanied by the vowel “A” but not any other vowel. Thus a word like “Yuvan” or “Yuuham” etc are sanskrit words.
(7) Rhyming in poetry is at the beginning of the line as opposed to other languages where the rhyming is at the end of the line!
(8) Rhyming is at the first letter or the second letter. For example if a line starts with “Kadhu” and the next line starts with “Kannu”, then these lines are considered to be rhyming because the first letter is “Ka”. This is called “Monai” or “agreeing”.
(9) Rhyming can also be at the second letter of the first word in each line. For example if the first line starts with “Mey” and the next starts with “Poy”, these are considered rhyming (note that the second letter in the words are “Y”). This type of rhyming is called “Edhukai” or “Opposing hands”).
(10) Olden day poetry was on either “known persons as heroes/heroins” or “Unknown persons as heroes/heroines”. The former is known as “Puram” poems (literally means outside / external) and the latter known as “Aham” (litterally means Inside / internal). Aham poems are considered more poetic and romantic.
(11) It has the letters “A” (as pronounced in the word Appu”), “I” (as pronounced in the word Important) and “E” (as pronounced in the word Elephant) to denote near objects, far objects and to ask questions. This is same as in Malayalam, Kannada and Telugu.
(12) Old Tamil did not have present tense, only past, near past and future. Present tense using “Kiru” and “Kindru” are improvisations from about 10th century on.
(13) Tamil has no word for the numeral zero. People use the English word “Cypher” or “Zero” or sometimes the Sanskrit word “Poojiyam”.
(14) The language is not a “prefixing” one one. It is almost always suffixing. For example in English, you would prefix “Dis” to the word “like” to say “dislike”. In Tamil, the word “alla” or “Illa” is suffixed to get the differentiation; Or these could be entirely different words. For example “Viruppu” means “like” and “Veruppu” means “Hate”/”dislike”. In Sanskrit “Dharmam” and “Adharmam” make a pair. In Tamil, the words are “Aram” and “Maram”.
(15) The gender and number are like resembling the usage in English. For example, a dog is addressed as an “it” and not as a “he” or a “she”. Also, all inanimate things are addressed as neutral gender unlike Hindi / Sanskrit.
14) Words for numerals show oddity at 9, 90, and 900. Literally the words for these three numbers has the meaning “Old ten”, “Old hundred” and “Old thousand”. (The current Tamil / Malayalam word Onbadhu for “nine” is a corruption of the word “Thonbadhu” which is still present in Telugu as “Thonmidhi”. In Tamil, “Thol” means “old”).
(15) Most old poetry are secular in nature. Though Gods and their names are mentioned, no great importance is given. The poetry which teach us “good” and “bad” are secular and absolute and not derived from Gods, Vedams etc.
Some or most of the linguistic basics above may actually be common to Malayalam, Kannada and Telugu because these are in one family.