Final answer:
The word 'sky' is a common noun, not a proper noun. Proper nouns are specific names for individuals, places, or things and always start with a capital letter. The term 'sky' is a general term for the expanse seen above the earth and doesn't denote a specific location or entity.
Step-by-step explanation:
The word 'sky' is not considered a proper noun. Proper nouns are specific names for particular people, places, or things. They always start with a capital letter. Examples of proper nouns would include the names of cities (e.g., New York, London), individuals' names (e.g., Sarah, John), and branded items (e.g., Nike, Apple). However, the term 'sky' is a general term referring to the expanse that is seen above the earth from a spectator's viewpoint no matter where one might be. The word 'sky' does not denote a specific geographic location or distinct entity and therefore is considered a common noun.
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