Sharpness; the quality of being sharp (a literary/Chinese-derived noun). In everyday speech, 鋭い or 鋭さ is more common.
古い漢文注には「鋭（えい）は刃の鋭さをいう」と説明がある。
An old Chinese commentary explains that '鋭 (ei)' means the sharpness of a blade.
A sharp weapon or blade (historical/literary usage).
古文書では短剣のことを『鋭（えい）』と記す場合がある。
In old documents, a dagger is sometimes referred to as '鋭 (ei)'.
A fine soldier or elite fighter (archaic expression).
戦記の注釈に、国の鋭（えい）を集めたとある。
A war chronicle's note says that the country's elite soldiers were assembled.