Refers to the quality of being thin or slender.
La tenuidad del hilo lo hacía perfecto para bordar detalles finos.
The thinness of the thread made it perfect for stitching fine details.
La tenuidad de sus brazos le daba una apariencia frágil, pero era muy fuerte.
The thinness of her arms gave her a fragile appearance, but she was very strong.