No, the word ‘day’ is not a proper noun. It is a common noun that refers to a period of 24 hours. Proper nouns, on the other hand, are specific names that refer to individual people, places, or organizations, like ‘Monday,’ ‘Sarah,’ or ‘New York.’
To elaborate, common nouns are general terms that can apply to any member of a class, such as ‘day,’ ‘city,’ or ‘dog.’ Proper nouns, in contrast, designate unique entities. When we say ‘Monday,’ we are referring to a specific day of the week, making it a proper noun. Similarly, if you refer to a specific day and give it a name, such as ‘Independence Day,’ then ‘Independence Day’ would be a proper noun, but ‘day’ by itself remains a common noun.