incompatibilist adjective 1noun 1forms 3 adjective1 •Of, pertaining to or supporting incompatibilism. noun1 •A proponent of incompatibilism.An incompatibilist need not be a libertarian but the incompatibilist is committed to saying that there are possible worlds where creatures more or less like us have free will. — 2007 formsincompatibilists · more incompatibilist · most incompatibilist