Know how to use "fewer" and "less"? Find out.
c.1300, "spider threads spun in fields of stubble in late fall," apparently from gos "goose" + sumer "summer" (cf. Swedish sommertrad "summer thread"). The reference might be to a fancied resemblance of the silk to goose down, or because geese are in season then. The German equivalent mädchensommer (literally "girls' summer") also has a sense of "Indian summer," and the English word originally may have referred to a warm spell in autumn before being transferred to a phenomenon especially noticable then. Cf. obsolete Scottish go-summer "period of summer-like weather in late autumn." Meaning "anything light or flimsy" is from c.1400. The adjective sense "filmy" is attested from 1802.