Can you use a colon to introduce just a single item instead of a list?

Solution 1:

The Oxford Guide to Style (2002) offers a usefully concise (but somewhat oddly punctuated) discussion of the colon at section 5.5:

5.5 Colon

The colon points forward: from a premise to a conclusion, from a cause to an effect, from an introduction to a main point; from a general statement to an example. It fulfills the same function as words such as namely, that is, as, for example, for instance, because, as follows, and therefore:

[Relevant example:] She had but one hobby: chocolate.

Various U.S. style guides adopt essentially the same view of the colon that Oxford does. All of them approve of the use of a colon to set off phrases such as the one in your example:

For three years, I ate hamburgers: my friend's favorite food.

Or, in Dan Bron's preferred formulation:

For three years, I ate my friend's favorite food: hamburgers.

Alternative punctuation options include an em dash:

For three years, I ate hamburgers—my friend's favorite food.

a comma:

For three years, I ate hamburgers, my friend's favorite food.

and (arguably) parentheses:

For three years, I ate hamburgers (my friend's favorite food).