Altweibersommer.

At least in the meaning "Indian summer", seemingly from alt (“old”) + Weiber (“women's”) + Sommer (“summer”), literally "old women's summer". Compare Hungarian vénasszonyok nyara, Polish babie lato, archaic Czech babské léto, Russian ба́бье ле́то (bábʹje léto), Belarusian ба́біна ле́та (bábina ljéta), Ukrainian ба́бине лі́то (bábyne líto), and English old wives' summer; compare also German Mädchensommer (literally “girls' summer”); the Polish and Czech terms for the season are also used for the webs. DWDS suggests the use for cobwebs could be comparing them to old women's white hair, like the name of the wood anemone, Altweibergras, and a regional name for cottongrass, alte Mägde. Alternatively, the middle element Weib may be a regional variant of Spinnwebe (“spider's web”) (cognate to English web), or related to weben (meaning, and related to, weave). Compare English gossamer, traditionally taken to be from "goose summer" and to have originally referred to the season (like Scots goesomer (“St Martin's summer”)) and then to webs; DWDS considers the connection of that word with summer and this word with Sommer (“summer”) uncertain, but besides other summery words for the webs like Sommerfäden (literally “summer threads”) (cognate to Dutch zomerdraden (literally “summer-threads”)), fliegender Sommer (“strands of web”), and Mariensommer, there are words like Herbstfäden (literally “autumn threads”).