i-adjective
Describes something physically small, thin, or fine-grained. Often used for objects, particles, or details.
この砂は粒が細い。
This sand has fine grains.
彼女は細い字を書く。
She writes in small characters.
i-adjective
Used for a person who is tight-fisted or unwilling to spend money. Often appears in casual or critical contexts.
あの人は金に細いから、割り勘にしよう。
That person is stingy with money, so let's split the bill.
The reading こまい is a variant of 細かい (こまかい), sharing the same root meaning of smallness. The exact historical derivation is uncertain.