also: すんぷん
noun, adverb
tiny bit; the slightest amount
Used in negative sentences to mean 'not even a tiny bit'. Often paired with 違わない, 狂わない, or 変わらない.
この時計は寸分の狂いもなく動いている。
This clock runs without the slightest deviation.
彼の説明は寸分違わず正しかった。
His explanation was exactly right, without a single error.
少しも is a more common and casual way to say 'not at all' or 'not even a little'. 寸分 is more emphatic and often used in formal or precise contexts.
Compound of 寸 (すん, a traditional unit of length, about 3.03 cm) and 分 (ぶん, one-tenth of a 寸), together meaning a very small amount.