This paper examines from a Cognitive Linguistic approach the polysemy of the GĩKũYũ nouns from the semantic field of celestial bodies namely: mweri “moon”, njata “star” and riua “sun”.These nouns have multiple meanings among them the literal and extended meanings. From the data analysis it was observed that the literal meanings of these nouns are extended to have related meanings which are found in the semantic fields of animals, human beings and seasons. Metaphor and metonymy are the two mechanisms that motivate formation of polysemous meanings from these nouns.