单词：re-entrant 

形容词

• 
  [1.a.re-entrant] (同义词:[re-entrant( adj. 凹的（角） )]  [reentrant(n.再进去, 凹角 adj. 再进去的, 凹角的 )]  )
• 
  注释列句：(of angles) pointing inward; "a polygon with re-entrant angles"
• 反义词 -> [salient( adj. 易见的, 显著的, 突出的, 跳跃的 n. 凸角, 突出部分 )]