Wanting to get into Tocharian, I was daunted by the seeming lack of an introductory textbook, which would necessitate the need to cobble together a view of the language from Pinault’s deceivingly titled Introduction au tokharien and Malzahn’s The Tocharian Verbal System, the only books on the subject I have at hand. I shouldn’t have neglected to search for online resources, for it turns out that the Indo-European team at the University of Texas at Austin has added a Tocharian course to their Early Indo-European Online series of language lessons.
The lessons have a useful appendix on looking up Tocharian words in a dictionary which begins as follows:
Let’s assume you have gotten enough Tocharian under your belt that you’re ready to move on to other texts. Chances are, you’re reading a Tocharian B text; so you place a document with the text on your desk, and beside it your steady companion, the venerable Dictionary of Tocharian B by Douglas Q. Adams. As you read, you come across the word B kelu. You have no recollection of this word, so you look it up in your dictionary. Interestingly, you find there is no listing for kelu, not even a hint like the helpfulq.v. …telling you where else you might look. Nothing. All you find in the near void of kel… entries is a word for ‘bellybutton’ and some term for ‘a medical ingredient’. Neither of these has a chance of giving you kelu, so you may wonder if it was really worth all the trouble learning this esoteric language in the first place. Now what? Search page by page through the section on k? Do you realize how many words start with k in Tocharian? No…
Your only sensible option is to devise some way of cutting down your work and honing in on some realistic possibilities. How to proceed? First, consider what you do know: kelu is not a headword. That is, it is not an adverb; it is not the nominative singular of a substantive; and it is not a verb form transparently displaying the basic verbal root from which it derives. So it must be some other inflected form: either a non-nominative case form, or one of the many possible conjugational forms of a verbal root. At this point, you may as well guess. The final ‑u of kelu reminds you of the preterite participle, and so you guess that what you’re confronted with is a verb form – maybe even a preterite participle, if you’re lucky. But from what verb?
This is where the extra time you spent learning Tocharian in light of historical linguistics finally pays off.
And indeed, the same diachronic insights that help for using a Tocharian dictionary here would apply equally well to Greek, at least for those lazy students who have never quite memorized the table of the major principle parts.