I'd like to know when to use italics and when to use single quotation marks should be used. For example:
The word he was looking for was ‘abjuration’.
The word he was looking for was abjuration.
I consulted The Oxford Guide to Style (2002) to see what a style guide focused on British English preferences had to say about using single quotation marks or using italics in instances involving what The Chicago Manual of Style refers to as "words used as words." OGS's guidelines are ... ambivalent.
On the one hand, in section 5.13.1 [Quotation marks:] Names and titles, OGS has this advice:
Use quotation marks to enclose an unfamiliar word or phrase, or one to be used in a technical sense. The effect is similar to that of highlighting a term through italics:
[Example:] 'Hermeneutics' is the usual term for such interpretation.
[Example:] Our subject is the age of Latin literature known as 'Silver'.
But on the other hand, in section 6.2.1 [Italic:] Emphasis and highlighting, OGS says this:
Parts of sentences can be highlighted by italics or by quotation marks. Decide which will be clearest and most intelligible to the reader, and apply that style consistently in comparable contexts:
[Examples:] the letter z[;] spell labour with a u[;] the past tense of go is went[;] the dos and don'ts
Technical terms and words being introduced, defined, or assigned a special meaning often need to be italicized at first mention:
[Example:] the doctrine of determinism
[Example:] the grapes next enter the crusher-stemmer
[Example:] the outing known as a wayzgoose is an old tradition
[Example:] here, the piunt-till is a box rather than a deck
So what rule does OGS recommend that you apply in choosing between 'abjuration' and abjuration? "Decide which [you think] will be clearest and most intelligible to the reader, and apply that style consistently in comparable cases." In short, either option is acceptable to Oxford, but be consistent about applying it.