• 索引さくいん — an index in a book
• 検索けんさく — to search, especially in data or on the web
• 捜索そうさく — a search for someone or something missing
• 思索しさく — deep thinking; philosophical reflection
• 模索もさく — groping and searching for a solution

The character combines the thread radical with a hand-based element: imagine drawing out and following a long cord. From the idea of tracing along a line or rope, the meaning expanded to searching, tracing, and probing for something.