noun
lawnmower
A machine for cutting grass, typically used in gardens or parks.
週末に芝刈り機で庭の芝生を刈った。
I mowed the lawn with a lawnmower on the weekend.
草刈り機 is a more general grass cutter or brush cutter, often used for taller weeds and rough areas, while 芝刈り機 specifically refers to a lawnmower for manicured lawns.
Compound of 芝 (しば, 'lawn grass'), 刈り (かり, noun form of 刈る 'to cut'), and 機 (き, 'machine').