24/7 is itself a word. There are many sources backing this up. I find it incredible yet expected that this is possible. Hopefully I'm not late to the party and everyone already knows 24/7 is an actual word.
Twenty-four hours a day, seven days a week; all the time
You just can’t afford to let things get you down, especially when you are on call 24/7.
Interestingly enough, this is a numeronym. Hopefully I'm not the only one who hasn't heard of this word either. The numerals are simply taking the place of twenty-four seven. Additionally, 24/7 is the only word I can find that makes use of any symbols other than letters and numerals.
Here's a definition of word to clarify how this can actually be a word:
1.1 - A single distinct conceptual unit of language, comprising inflected and variant forms
So 24/7 is definitely a concept expressing the consistency or continuity of something.
I should note that it's extremely rare for a word consisting of just numerals and symbols to appear in a highly regarded dictionary. Maybe I'm just crazy.