Today, searching for the term "cloak", I came across these definitions
From Longman DOCE 5th Ed.
cloak noun [singular] an organization, activity, or way of behaving that deliberately protects someone or keeps something secret
From Oxford Advanced Learners Dictionary 8th Ed.
cloak noun singular (literary) a thing that hides or covers sb/sth
I really expected to see "uncountable" rather than "singular" for this meaning. What difference between the two noun types that I am missing?
The important part is "a thing". If you have more than one cloak, you can count up the number of them you have.
Uncountable nouns are things like water, milk, sand...anything you can't quantify. I can say
I bought three cloaks.
But I can't say
We have five milk in the fridge.
In general "uncountable" nouns are not preceded by the indefinite article. Many of them are mass nouns, such as water, or abstract nouns, such as anger. See this description of them from edufind's "English Grammar" section: Countable and uncountable nouns
The metaphorical use of cloak is generally not used in the plural. But it behaves differently from the class of nouns that we normally call "uncountable": you cannot use it without an article. The Oxford Learner's Dictionary gives the example sentence "The author prefers to hide behind a cloak of anonymity." It would be ungrammatical to say *"The author prefers to hide behind cloak of anonymity."
