root cause

/R UW1 T K AA0 Z/
noun
  1. 1

    An initiating cause of a chain of events which leads to an outcome or effect of interest.

verb
  1. 1

    The action of identifying the cause of a chain of events which leads to an outcome or effect of interest. To root cause something's root cause does not necessarily imply the use of root cause analysis (RCA).

Source: https://en.wiktionary.org/wiki/root%20cause