verb

make or become smaller or fewer in size, amount, intensity, or degree.

the population of the area has decreased radically

lessen,grow/become less,grow/become smaller,reduce,drop,diminish,decline,dwindle,contract,shrink,fall off,die down,abate,subside,let up,tail off,ebb,wane,taper off,peter out,lighten,sink,slump,plummet,plunge,make less/fewer,lower,cut down/back (on),cut,curtail,narrow,pare down,slim down,tone down,temper,weaken,deplete,minimize,slash