Collins Concise English Dictionary © HarperCollins Publishers::
pile on(tr, adverb) to add in large amounts: to pile on more rice, to pile on the agony(intransitive) to jump on top of a person or group of people(intransitive) to criticize a person who has already been subjected to criticism by otherspile it on ⇒ to exaggeratepile-on an act or instance of criticizing a person who has already been subjected to criticism by others
'pile on' also found in these entries (note: many are not synonyms or translations):