From Longman Dictionary of Contemporary Englishlawn mowerˈlawn ˌmower noun [countable] 
DLGa machine that you use to cut grass
DLGa machine that you use to cut grassExamples from the Corpus
lawn mower• I even bought a lawn mower.• At 95 decibels, about the sound level of a lawn mower, workers are allowed four hours' exposure.• I found it thus: I had never ridden a lawn mower before.• A lawn mower droned a few houses down.• His dad can stand her for about five minutes, then he goes out and starts up the lawn mower. 