Learn English – Difference between online and on line

word-difference

When do we use online as one word and when as two words?
For example, do we say :"I want to go online or on line?"

Best Answer

When the internet was more of a novelty, it seems like both forms were used. The two words were often hyphenated as well. For example, the following is a screen shot from a 1997 book entitled The Future of Money in the Information Age.

https://books.google.com/ngrams/graph?content=getting+on+line%2C+getting+on-line%2C+getting+online&year_start=1980&year_end=2000&corpus=15&smoothing=3

And a 1992 book reads:

Once you have a valid BBS number, it's time to dial it and get on line.

That said, it looks like the single-word form is winning out, though. It's far easier to find examples where online is a single word. Check out the Ngram.

It may be worth noting that such neologisms are not uncommon in the technology realm; here is a similar Ngram showing how username is becoming a single word.