The aim of this paper is to construe neutralization of Korean dimensional adjectives based on metonymy. All our knowledge of the world is a structured frame, that is to say an idealized cognitive model. In this paper, a viewpoint of the dimensional adjectives is that the frame or the idealized cognitive model is a whole with parts. The frame is conceptualized as the whole with parts, so it gives rise to a metonymy relationship of whole and parts form and part and part form. The metonymy, a very essential and conceptual mechanism in a human thinking and language, is a cognitive method that is foregrounding a source and backgrounding a goal to reflect in a concept structure of the goal. In other world, the metonymy is a cognitive process that if two substances in a same one area are in a relation of contiguity, one substances ``media`` rouses a mental approach to the other substance ``goal``. In the last study, the Korean dimensional adjective is showed that each a supra-terms and sub-terms are consist of contraposition of unmarkedness and markedness, and appear as a neutralized term. This study shows that the neutralization of the Korean dimensional adjective is from the metonymy and cognitive things are its cause, so it is the problem of degree. The metonymic relation which is the parts representing the whole, in other word, the dimensional adjective which uses the supra-terms representing a whole criterion, is for ``length, height, depth, width, thickness, size`` out of eight pairs excepting ``distance.`` On the contrary, the metonymic relation which is the whole representing the parts, ``distance`` is an example of the term representing the whole criterion which is used as the supra-terms. Based on the metonymy, there is a neutralized term that the part represents the whole or the whole represents the part, and therefore there is a difference in degree. The supra-terms length, height, depth, width recognized as a basic level is clearly marked down as the neutralized term, but thickness, size, distance which is not recognized as the level, is not distinctly cognized. In addition, the reason why the supra-terms is not neutralized in ``far or distant/close or near`` is that ``distance`` is a concept of ``length``. ``Length`` is recognized as the basic level, so it is left a blank space in the position of ``distance``. Furthermore, it is more complicated in two dimensions than one dimension and three dimensions more than two dimensions. For this reason of a cognitive salience, ``thick`` is not appeared noticeably in ``thick:small/thin`` and ``big`` is not appeared conspicuously in ``big/small``. The frequently used words seem to be recognized more clearly by language users, the cognitive salience also appears in a word order.