What part of speech is 'son'?

Answer 1

Son is a noun.

Quite a good test of a noun is whether you can pair it with the or a or an. Examples of nouns:

the desk

a baker

a feeling of happiness

That last example shows a limitation of this test. The word feeling can have an article (a or the) in front of it. Abstract nouns like happiness do not pass the test, or at least not so obviously. (If you work at it, you can come up with a sentence using the before happiness:

He felt the happiness that comes at the end of a large project well done.)

Ultimately, the idea of a noun is that it refers to a "thing", which may be concrete, like a desk, or abstract, like feelings and happiness.