Definition of flatline verb from the Oxford Advanced American Dictionary

     

    flatline

     verb
    verb
    NAmE//ˈflætlaɪn//
     
    (informal)Verb Forms present simple I / you / we / they flatline
     
    he / she / it flatlines
     
    past simple flatlined
     
    -ing form flatlining
     
     
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  1. 1[intransitive] to die
  2. 2[intransitive] to be at a low level and fail to improve or increase He said the party had been “flatlining” — failing to increase its level of support — for eight years.
See the Oxford Advanced Learner's Dictionary entry: flatline