I’ve seen all three versions for describing a person on stage performing comedy: “stand up”, “standup”, and “stand-up”.
My guess is that the term started as two words, but as the performance form itself became more established in the culture, the set of the two words together became perceived as a single unit. Reflecting that, in writing, some people even started merging the words or joining them with a hyphen.
Based on that assumption, I’m extrapolating that it’s a term in the midst of evolving, and so maybe there might not be an absolute answer on this.
Still, I’d like to be consistent myself and settle on one. Is there any particular reason I should choose one over the others?
The Guardian Style Guide says:
adjective, as in a standup comedian performing standup comedy; and noun: a standup performing standup
Generally, it’s a matter of grammar whether to space words or hyphenate. And generally, it’s a matter of style or usage whether to hyphenate or join the words together.
I log in to my computer and enter my login details.
Here log in is an action, and login describes my personal details. Login could be hyphenated, and often hyphenated words lose their hyphen over time and with use. We used to say to-day and to-morrow.
The Guardian Style Guide again:
Our style is to use one word wherever possible. Hyphens tend to clutter up text (particularly when the computer breaks already hyphenated words at the end of lines). This is a widespread trend in the language: “The transition from space to hyphen to close juxtaposition reflects the progressive institutionalisation of the compound,” as Rodney Huddleston puts it, in his inimitable pithy style, in his Introduction to the Grammar of English.
See the rest of their hyphen entry for more.