The word ‘uncle’ is not a proper noun; it is a common noun. Common nouns refer to general items, people, or concepts, while proper nouns name specific individuals, places, or organizations.
For example, in the sentence ‘My uncle is visiting today,’ the word ‘uncle’ describes a general relation and does not specify which uncle is being referred to. However, if you say ‘Uncle John is visiting today,’ then ‘Uncle John’ becomes a proper noun because it identifies a specific person.
In summary, ‘uncle’ on its own is a common noun, but can become part of a proper noun when used with a specific name.