also: クモのいと
noun
spider's thread; spider silk
Refers to the silk thread produced by spiders, used for webs, draglines, etc.
蜘蛛の糸は鋼鉄よりも強いと言われている。
Spider silk is said to be stronger than steel.
朝露に濡れた蜘蛛の糸がキラキラ光っていた。
The spider's thread, wet with morning dew, was sparkling.
蜘蛛の巣 means 'spider web' (the structure), while 蜘蛛の糸 refers specifically to the silk thread itself.
Compound of 蜘蛛 (kumo, 'spider') + の (possessive particle) + 糸 (ito, 'thread'). The reading くものいと is a straightforward combination.