Is a 14-month-old able to understand what "no" means?
You're correct that "no" is a difficult concept for a 1-year-old child to make sense of. What you're describing sounds perfectly normal. So the best thing to change here is not your son's behavior but your expectationsespecially since your son is likely to test limits even more in another year.
At this age, your primary concern should be your son's safety, not his immediate obedience. You achieve that by making his environment safe, not by saying no to dangerous activities. That makes it easier on everyone.
Remember that a certain amount of testing limits by children not only is healthy, it's absolutely necessary. That's how they internalize the discipline we're trying to teach.
It sounds as if, from your child's perspective, getting you to say "no" is a delightful game and a great way for him to get some extra attention. Why not turn this in your favor by looking for situations in which you can say "yes" instead of "no." Give him the extra attention that way, and you'll both have more fun.