hangnail       
noun [ C ] uk/ˈhæŋ.neɪl/ us/ˈhæŋ.neɪl/
 甲刺,倒刺
a small piece of torn skin at the edge of a fingernail
  I had a hangnail that was really hurting me. 我有一个倒刺,让我觉得非常疼。 
 - More examples
 - Picking, biting, or cutting a hangnail may put you at risk of infection.
 - We encourage people not to go to the doctor for every hangnail.
 - There's no shortage of folk remedies reputed to cure everything from headaches to hangnails.
 - In a time in the NFL's history where a guy won't play if he's got a hangnail, this guy will play if his arm is hanging off.
 - There was a hangnail at the side of my thumb and I tore it off.