adjective.
Of or stating the characteristicfeature of a proposition that is necessary (or impossible), perfectlycertain (or inconceivable) or incontrovertiblytrue (or false).
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
adjective.
of a proposition; necessarily true or logically certain
Word Usage
"For geometrical principles are always apodeictic, that is, united with the consciousness of their necessity, as: "Space has only three dimensions.""