verb

become progressively worse.

relations between the countries had deteriorated sharply

worsen,get worse,decline,be in decline,degenerate,decay,collapse,fail,fall,drop,sink,slump,slip,slide,go downhill,go backwards,go to rack and ruin,stagnate,wane,ebb,go to pot,go to the dogs,hit the skids,go down the toilet,go down the tubes,go to the pack,retrograde,degrade,break down,decompose,rot,putrefy,go bad,go off,spoil,perish,wither,atrophy,weaken,fade,break up,disintegrate,become dilapidated,crumble,fall down,fall apart,fall to pieces,corrupt