grass sickle
A sickle specifically for cutting grass; a rare term, with 草刈鎌 (くさかりがま) being more common.
See also: 草刈り鎌
祖父は草鎌で庭の草を刈っていた。
My grandfather was cutting the grass in the garden with a grass sickle.
Compound of 草 (くさ, 'grass') and 鎌 (かま, 'sickle').