retardation retardation /riːtɑːrˈdeɪʃən/

noun

1. () A decrease in rate of change  ( retardation , deceleration , slowing )
   a decrease in rate of change
    The deceleration of the arms race
   the deceleration of the arms race
   
2. The act of slowing down or falling behind  ( retardation , slowdown , lag )
   the act of slowing down or falling behind
   
3. Lack of normal development of intellectual capacities  ( backwardness , mental retardation , retardation , slowness , subnormality )
   lack of normal development of intellectual capacities
   
4. Any agent that retards, delays or hinders  ( retardant , retardation , retardent )
   any agent that retards, delays or hinders
    Flame-retardant
   flame-retardant
   
5. The extent to which something is delayed or held back  ( retardation )
   the extent to which something is delayed or held back