ploughsharePronunciation: /ˈplaʊʃɛː/ (US plowshare)Definition of ploughshare noun the main cutting blade of a plough, behind the coulter. Origin: late Middle English: from plough + Old English scær, scear 'ploughshare' (related to shear)ploughshare in other Oxford dictionaries Definition of ploughshare in the US English dictionary