/ ˈpærəpɪt; NAmE ; -pet/ noun
a low wall along the edge of a bridge, a roof, etc. to stop people from falling :
( figurative )
He was not prepared to put his head above the parapet and say what he really thought (= he did not want to risk doing it) .
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WORD ORIGIN
late 16th cent.: from French , or from Italian parapetto chest-high wall, from para- protecting + petto chest (from Latin pectus ).