Hi,
The first part of the sentence you quoted (guṇas tv āvṛtti-tantuṣu) is from a lexicon, though I am not sure immediately which one. So, rather than āvṛtti and tantu being coordinated meanings like "warp" and "weft," they are simply two unrelated meanings in which the word guṇa occurs, namely "repetition," i.e. "multiplication" (āvṛtti) and "thread" (tantu), with no particular specificity in the latter case of which kind of thread in a woven fabric.
"Thread" is, of course, a simple sense of guṇa, and one sees in mathematical literature that guṇa is the word used for multiplication.
I hope this helps.
Best,
Dave
--
David Buchta, PhD
Senior Lecturer in Sanskrit
Department of Classics
Brown University