Describes something done or felt privately, without others knowing. Often used for emotions, efforts, or struggles kept to oneself. The form is pre-noun adjectival (rentaishi), so it directly modifies a noun.
Compound of 人 (ひと, 'person') + 知れ (しれ, the 未然形 (mizenkei) of 知れる, 'to become known') + ぬ (classical negative auxiliary). Literally 'not known to people'.
