An atom's weight of philology

One of the oldest motivations for studying the history of language is to better study the fixed texts of holy books or classics. We try to learn from such texts, but without an understanding of philology we misread them - because, while the words have remained the same, their content has changed. Ibn Quraysh is one case in point; Ruskin offers another:

"[I]n languages so mongrel of breed as the English, there is a fatal power of equivocation put into men's hands, almost whether they will or no, in being able to use Greek or Latin words for an idea when they want it to be awful [ie impressive]; and Saxon or otherwise common words when they want it to be vulgar… [C]onsider what effect has been produced on the English vulgar mind by the use of the sonorous Latin form "damn", in translating the Greek katakrínō, when people charitably wish to make it forcible; and the substitution of the temperate "condemn" for it, when they choose to keep it gentle; and what notable sermons have been preached by illiterate clergymen on - "He that believeth not shall be damned"; though they would shrink in horror from translating Heb. xi. 7, "The saving of his house, by which he damned the world"… "

Standard Arabic has no layer of prestige loanwords corresponding to Greek and Latin words in English - all the classics of the Arab world are themselves in Arabic, and great efforts have been expended to keep the grammar of Standard Arabic roughly constant since the pre-Islamic era. But, thanks to the many new meanings conferred upon old terms during episodes of massive translation - both in the modern era and the Abbasid era - it is fairly susceptible to another of Ruskin's complaints: misinterpreting the words of old texts thanks to their modern meanings.

Once a medical student at Cambridge told me in all seriousness that the Qur'ān anticipated modern science by centuries in mentioning the "atom" (فمن يعمل مثقال ذرة خيرا يره, "for he who does an atom's weight of good shall see it")! Of course, every modern educated Arab knows that a ذرة dharrah is an atom. But looking at a pre-modern dictionary, such as Lisān al-`Arab, gives a rather different picture: a dharrah then was a type of small red ant, a weight equivalent to 1/100 of a barley grain, or a mote of dust (as seen in sunbeams), not an elementary particle of which all matter is composed. In parts of Sudan the first of those meanings is still in regular use: dirr there means a type of ant. But elsewhere they all seem to have faded from away from popular speech.

If I were interested in an English word, I could easily look it up in the OED and find a complete history of its different meanings and the dates at which they were attested. But for Arabic no such dictionary exists; to figure out when and how dharrah came to mean "atom" in the modern sense, I would have to look through a bunch of pre-modern works, or find an article on the subject. It's a gap that would be well worth filling.