WordWeb Online

1. [informal] Cease to live; lose all bodily attributes and functions necessary to sustain life
   - die, decease [archaic], perish, go, exit, pass away, expire, pass, kick the bucket [informal], cash in one's chips [informal], buy the farm [N. Amer, informal], conk [informal], give-up the ghost [informal], drop dead, pop off [informal], choke, croak [informal], snuff it [informal], cop it [Brit, informal], cash in [informal], pop one's clogs [informal]
    
2. Remain at a low level without increasing
   "the shares flatlined"

Derived forms: flatlined, flatlines, flatlining

Type of: change state, turn

Encyclopedia: Flatline