tense up

Verb

• cause to be tense and uneasy or nervous or anxious
  • he got a phone call from his lawyer that tensed him up
    

• become tense, nervous, or uneasy
  • He tensed up when he saw his opponent enter the room
    

Related words

• Synonyms: 
  tense , strain
• Antonyms: 
  relax , unstrain , unlax , loosen up , unwind , make relaxed , unbend , decompress , slow down