Usage of articals. e.g. When do we use a singular noun on its own without an article?

Question

2 questions.

Q1. Earlier these days, I saw the usage of "Leader of ...", which is a countable noun without a preceding article. Is that grammatically correct?

What I found in oxford guide to english grammar:

A singular noun on its own • 167

We use a singular noun on its own only in some special patterns.

However, further explanation is not given in that pdf.

Then I found another pdf: esl article usage rules. But I didn't find the usage of "Leader of ..." in it.

So, is the last pdf accurate?

Q2. "a becoming humility"(article before uncountable noun) is OK.

My answer to another question referring to A | meaning in the Cambridge English Dictionary:

used before some uncountable nouns when you want to limit their meaning in some way, such as when describing them more completely or referring to one example of them:

I only have a limited knowledge of Spanish.

He has a great love of music.

There was a fierceness in her voice.

But in the last pdf esl article usage rules, an article before "thing"(a countable noun) can be omitted:

Rule 37: Use Ø when generalizing about abstract nouns.

ex: Love is beautiful thing.

Is that correct?

Answer 1

The explanation given in the Oxford Guide to English Grammar ("We use a singular noun on its own only in some special patterns") is not particularly useful. More helpful is the following extract from Collins Cobuild English Guides 3: Articles (p50) in the section called Special Roles:

Some nouns can refer to a special, unique role held by a person in a particular situation (for example, a government or business). When they are used like this, you can leave out the definite article.

• ...when he was President.
• It was nearly 40 years before she became Queen.
• ...Mr John Hume, leader of the Social and Democratic Labour Party.

The Guide goes on to list numerous examples of 'special roles' (including captain, chair, boss, treasurer, director, author), and concludes:

Note that when you are talking about a person rather than describing someone's role you need an article.

• The President had issued a sympathetic reply.
• The Queen then abandoned the project.

Since you have not included the sentence in which you saw the words Leader of..., it is not possible to say definitively if the definite article is needed or not.

Finally, a comment: Your Q2 is best asked as a separate question.