In the definition for “floss” this statement is somewhat non sequitur, tossed into the middle of the definition, with an implied association to what comes after that isn’t quite accurate.
" In “The Mill on the Floss” the word is the proper name of a fictitious river in the English Midlands. "
I have read this book and I’m pretty sure the name and meaning come from the German sense of the word “floss” as in “fluss” (river, flow). It has nothing to do with silk thread which follows the sentence somewhat anomalously. This definitely would read better if it were slightly rewritten (with regard to The Mill on the Floss reference) and if there were a bigger break between The Mill on the Floss reference and the following list (e.g., silk thread).
Also, the sense of the similarity between river and floss (as in threads) is closer to our English word “strand”. A strand of wool, thread, floss, is long and wavy like the course of a river. This association could possibly be included in the definition since the way it reads now, it jumps from river to thread and omits mentioning the connecting link, which is the conceptual sense of a ‘strand’.