► 動詞油断  [ゆだん]  [
油断する]    
meaning:  relax  rank: 2☆ 
彼等は
敵が油断したところに
攻撃をかけた ⇨ They attacked the enemy when they let their guard down  
(☛ Letting your guard down when you shouldn’t)► 名詞油断  [ゆだん]    
meaning:  relax  rank: 2☆ 油断は
禁物だ ⇨ Never let your guard down  
(☛ Letting your guard down when you shouldn’t)More examples:- 彼等は敵が油断した隙を突いて攻撃をかけた ⇨ They exploited a tiny opportunity when the enemy let the guard down and attacked