Refers to the initial stage or the very beginning of something, often implying a small opening that leads to a larger development. Common in phrases like 糸口を見つける (find a starting point) or 糸口をつかむ (get a foothold).
I can't find a starting point for solving the problem.
彼の一言が事件解決の糸口となった。
His single remark became the first step toward solving the case.
Used when a small piece of information or a trace provides a way into understanding or solving something. Often overlaps with sense 1, but emphasizes the clue-like nature.
警察はまだ有力な糸口をつかんでいない。
The police haven't yet found a solid lead.
そのメモが謎を解く糸口になった。
The memo became a clue to solving the mystery.
thread end
Literal meaning: the end of a thread. This is the original, concrete sense, but it is rarely used in modern everyday conversation. Mostly encountered in explanations of the word's origin or in literary contexts.
「糸口」の文字通りの意味は、糸の端のことだ。
The literal meaning of 糸口 is the end of a thread.
He found a clue that could lead to economic recovery.
I couldn't find a way to start the conversation.
The case went cold, and there wasn't even a hint of a lead.
端緒 is a more formal, literary word for the very beginning or first clue of a matter, while 糸口 is the everyday word for the same idea.