commonest

belonging to or participated in by a community as a whole; public;
having no special distinction or quality; widely known or commonly encountered; average or ordinary or usual;
common to or shared by two or more parties;
commonly encountered;
being or characteristic of or appropriate to everyday language;
of or associated with the great masses of people;
of low or inferior quality or value;
lacking refinement or cultivation or taste;
to be expected; standard;

commonest is a valid Scrabble (US) TWL word

commonest is a valid Scrabble Word in Merriam-Webster MW Dictionary

commonest is a valid Scrabble Word in International Collins CSW Dictionary

commonest is a valid Words With Friends word