on-call
 /ˌɒn ˈkɔːl/
  /ˌɑːn ˈkɔːl/
[only before noun] (especially North American English)- (of a doctor, police officer, etc.医生、警察等 (尤指紧急情况下)随叫随到的 - on-call doctors随时应诊的医生 
 
- on-call doctors