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small; little
「細」 has other readings with different meanings.
細なことでも気になる性格なのです。
I have a personality that worries about even small things.
細な声で何か呟いているのが聞こえた。
I heard a tiny voice mumbling something.
細な変化にも気づける観察力が必要だ。
You need the ability to notice even small changes.