• 糸いと — thread
• 毛糸けいと — wool yarn
• 糸口いとぐち — clue; starting point
• 糸電話いとでんわ — string telephone
• 絹糸けんし — silk thread
• 縫ぬい糸いと — sewing thread

“糸” originated as a pictograph of twisted thread. It appears in many words related to sewing and weaving, and it also works metaphorically in expressions like 糸口, meaning a clue or starting point.