A somewhat older or more casual word for a dictionary, especially a Japanese-language dictionary. Often used in compound words like 国語字引 (Japanese dictionary) or 漢和字引 (Kanji-Japanese dictionary). In modern Japanese, 辞書 (じしょ) is more common.
When I was a child, I used a dictionary to look up kanji.
この字引は古いけど、まだ役に立つ。
This dictionary is old, but it's still useful.
I looked up the kanji I didn't know in a dictionary.
I tried looking up the meaning of this word in a dictionary.