What words do people use interchangeably, but really mean two different things, but are very similar?

I’ll give you some examples:

Dizzy and light headed. You can be both, but one is your world is spinning. The other is you need to put your head down or you might pass out.

Another is cold and flu. Cold is stuffy, no fever (in adults) still can get out of bed. Flu is high fever, body aches, barely can move out of bed, sometimes a cough, very little to no congestion.

Stomach organ pain and stomach pain. The stomach organ is actually high up in the digestive system, kind of behind the left breast. The stomach is also used to refer to the front part of the waist.