I asked Venerable U Nandamaalaabhiva.msa for some clarification and
what he told me is very similar to Jim's explanations. Dhaatu has the
meaning of root indeed.
So the questioon could be "In what sense (or in which sense)
is "dhaatu" called "dhaatu"". And the answer "A root is what bears
its own meaning."
If we take gacchati (gamu + a + ti) for example, a is paccaya
(conjugational sign), 'ti' is aakhyaatavibhatti and has the three
meanings of tense (present), person (third person) and number
(plural), and gamu just bears its own meaning 'go' or 'to go'.
He also mentioned that he recently compiled and published a
reorganized version of the of the dhaatumaalaa part of the Saddaniiti
(in Burmese script) according to the alphabetical order. He gave the
title of Dhaatudiipaka (explanation or clarification of dhaatu) and I
suppose it would be quite easy to transcribe it in roman characters.
The Saddaniiti is still very much studied in Myanmar and until not
such a long time ago the late Venerable U Silananda was teaching it
in the United States along with the Padaruupasiddhi. There is
actually a quite interesting e-book called Paa.li roots which was
written by U Silananda and his assistant U Nandisena (the Argentinian
monk who also translated the Kaccayana in English as mentioned in an
earlier post) and which is available in this group's files. The full
title is "Pali Roots in Saddaniiti Dhaatu-Maalaa compared with
Paa.niniiya-Dhaatupaa.tha" and gives the meaning of the roots in
English, Spanish and Sanskrit.
Lastly I would like to quote Mabel Bode's invaluable book, "The Pali
litterature of Burma", pp16-17:
"During the reigns of Anorata's [the Burmese king who forcefully
brought Theravada Buddhism to Burma from the Talaing or Mon kingdom]
immediate successors learning took firm root at Pagan, and in the
year 1154 the monk Aggava.msa completed the Saddaniiti, a grammar of
the Tipi.taka, described as 'the most comprehensive in existence' [by
Charles Duroiselle]. It established the reputation of Burmese
scholarship in that age and the fame of the author to the present
day, for the Saddaniiti is still republished in Burma as a classic.
[...].
Aggava.msa was tutor to King Narapatisithu (AD 1167-1202), a powerful
and peacable monarch, whose reign was the most prosperous epoch in
the history of the kingdom of Pagan. According to the Gandhava.msa,
Aggava.msa was of Jambudiipa [actually the Burmese sometimes include
Burma or Aparanta, into India or Jambudiipa]. Forchhammer mentions
him among the famous residents in the retired monastery on the
Northern plateau above Pagan, 'the cradle of Pali-Burmese literature.'
The Saddaniiti was the first return gift of Burma to Ceylon. A few
years after its completion the thera Uttaraajiiva left Pagan and
crossed the sea to visit the celebrated Mahaavihaara, taking with him
a copy of the Saddaniiti, which was received with enthusiastic
admiration, and declared superior to any work of the kind written by
Sinhalese scholars."