With or without hyphen? non linear, non-linear or nonlinear?

This is my first post here and I have a question on the proper writing of some terms.

Is it “non linear”, “non-linear” or “nonlinear”? The same goes for:
on board, on-board, onboard
real time, real-time, realtime
on line, on-line, online

As far as I know the first version should be the right one except in cases where the meaning of the sentence would be ambiguous, e.g.
“real time system” could mean a time system that is real or a system that works in real time (not the best example, I know), so “real-time system” would be preferred.

A web search in scientific literature showed that all three variants are in use with probably “nonlinear” as the most popular. Since I am not a native speaker, I was wondering which one is the correct (if any).

Thank you


Hello Skad, I would use the hyphen to join two words that are used in everyday conversation in English, but may cause confusion for a non-native reader.

jack-pot, rather than jackpot.




happy-go-lucky, and so on.

Just use it. No-one will take exception to it. There are no fixed rules about doing so.


Hi, Skad. Basically, adding a hypen is British English, e.g., non-linear, while its close-up counterpart “nonlinear” is American English. Another usage of a hyphen is for clarity. A good example of it is your “real time system” versus “real-time system.” So it depends on the writer which style to use, unless there is a specific style that one person or group of people is following, e.g., The Chicago Manual of Style, which generally follows the American style.

I hope this helps.