Are uncountable nouns always abstract?

A singular noun refers to one person, place, thing or idea, whereas, plural noun refers to more than one person, place, idea or things. For example 'cat', 'house', 'book' presents singular form and to indictae more than one thing or plural form, it will be written as 'cats', 'houses' and 'books'. While forming the plural form of singular nouns, candidates must abide with the grammatical rules. 

A compound noun is a noun formed by combination of two or more nouns to create a new meaning. For example, when we combine two nouns 'air' and 'plane' it forms a compound noun 'airplane'. Other examples are:

• Bookshop: book and shop
• Rainbow: rain and bow
• Sunflower: sun and flower

Nouns are important because they talk about people, place, things or ideas. Nouns acts as foundation in a sentence by acting as subject, verb and more. Without a noun in a sentence, it would look vague and incomplete. Nouns gives identification, builds sentence, acts as subject, and provides clarity.

• Countable nouns are things that can be counted as seperate items like two books, three pencils, five students. Whereas, uncountable nouns are nouncs which cannot be counted like water, hair, milk, etc.
• Countable nouns have both singular and plural forms, whereas, uncountable nouns does not have singular or plural forms. 

This is something that depends upon the person and the context, so to identify an uncountable noun, first ask yourself: Can I count it in separate units? Does it have a plural form? If not, it's likely uncountable. For example, “furniture” cannot be made plural, and we don't say “two furniture.” We say “a piece of furniture” or “some furniture” instead.