spontaneous spontaneous /spɑːnˈteɪniːəs/

adjective

1. () Happening or arising without apparent external cause  ( self-generated , spontaneous )
   happening or arising without apparent external cause
    Spontaneous laughter
   spontaneous laughter
    Spontaneous combustion
   spontaneous combustion
    A spontaneous abortion
   a spontaneous abortion
   
2. Said or done without having been planned or written in advance  ( ad-lib , spontaneous , unwritten )
   said or done without having been planned or written in advance
    He made a few ad-lib remarks
   he made a few ad-lib remarks