Analysis of information sources in references of the Wikipedia article "Czechs" in English language version.
As Spal has observed, the origin of Čech (Bohemian) is far from clear, but amongst the more plausible explanations is that it has the root čel, as in čeleď (family), and also člověk (person).
The origin of the ethnonym Čech (Česi or Čechové in plural) is not entirely clear.