形容詞 unprovoked:

1. occurring without motivation or provocation- F.D.Roosevelt
   同義詞：motiveless, wanton

1. The boys' attack on the old woman was quite unprovoked.
   那幫男孩對老婦人的襲擊完全是無來由的。
2. I ask that the Congress declare that since the unprovoked and dastardly attack by Japan on Sunday December7,1941, a state of war has existed between the United States and the Japanese Empire.
   我要求國會(huì)宣布：由于日本在1941年12月7日星期日對我國無故進(jìn)行卑鄙的襲擊，美國同日本已經(jīng)處于戰(zhàn)爭狀態(tài)。
3. An unprovoked attack.
   未經(jīng)挑釁就發(fā)動(dòng)的進(jìn)攻