drop-off in WordNet English dictionary

1. a steep high face of rock
   "he stood on a high cliff overlooking the town"; "a steep drop"
   cliff  drop  drop-off 
   
2. a change downward
   "there was a decrease in his temperature as the fever subsided"; "there was a sharp drop-off in sales"
   decrease  lessening  drop-off 
   
3. a noticeable deterioration in performance or quality
   "the team went into a slump"; "a gradual slack in output"; "a drop-off in attendance"; "a falloff in quality"
   slump  slack  drop-off  falloff  falling off 
   

drop-off in English Wiktionary