perfunctory vs tip of the iceberg

perfunctory

adj
  • Performed in a careless or indifferent manner as a thing of rote. 

  • Done only or merely to conform to a minimal standard or to fulfill a protocol or presumptive duty. 

tip of the iceberg

noun
  • A small indication of a larger possibility; the first part encountered of a problem that is much bigger than it seems. 

How often have the words perfunctory and tip of the iceberg occurred in a corpus of books? (source: Google Ngram Viewer )