Signaling and signalling both describe the sending or use of signals to communicate, from cell biology to railway systems. Signaling is the single-L American spelling; signalling doubles the L in British English, matching the pattern of labelled and modelling.
The core difference
The single-L and double-L forms are regional spellings of the same word, not different concepts.
- signaling — American spelling, often used for biological or electronic signal transmission: Cell signaling controls how the body responds to hormones.
- signalling — British spelling, common in telecommunications and transport contexts: A signalling fault delayed several trains on the line.
How to tell them apart
Both spellings describe the same underlying idea, signals being sent and used to communicate, whether that is a cell responding to a hormone or a railway network coordinating trains. Which spelling turns up in a given field often just reflects where the writing originated, since British transport writing uses signalling constantly while American biology papers favour signaling.
As with other British double-L words, the trap is a spell-checker set to the wrong regional dictionary quietly swapping one spelling for the other mid-document. Keeping the language setting consistent, and doing one pass to check it, catches the slip before publication.
