I'm editing an advanced grammar text book and the author and I cannot decide on whether "reign" is an uncountable noun or not.
The sentence is:
With Mr Smith gone, her reign could begin.
Oxford Dictionaries define reign as:
1. (noun) The period of rule of a monarch:
“the original chapel was built in the reign of Charles I”1.1 The period during which someone or something is predominant or pre-eminent:
“she was hoping for a long reign as world champion.”
The author has identified other words in the passage as uncountable, e.g. meditation, activity, emptiness, slate, glass, silence, but not reign.