A hill is whatever you want to label a hill and, due to the subjective nature of this labelling, I think we need to create further categories to better enable understanding amongst differing levels of cyclist. To this end I think that a double descriptor approach is required, one for the hill and one for the cyclist passing on their subjective view. As this all gets more familiar it may be possible to just look at the cyclist descriptor to decide on whether to obtain their subjective view. This sounds very complicated but is actually quite simple:-
hill descriptors - on a scale ranging from 'might kill you' to 'you may not even know you went up it' - the interim level descriptors are variable and so too many to list, but we all get the gist
cyclist descriptors - on a scale ranging from 'Total Novice' to 'Cockwomble' - again too many interim levels to list but some noteworthy entires would be things like, 'Fatbloke', 'Mr Reasonable', 'Fixie Monster', 'I Only Have a Big Ring', 'My Slower Vehicle is a Porsche', 'Look at ME and Tremble' and my personal favourite 'I Put Out More Watts Than Battersea Powerstation'.
Taking a sample hill, familiar to us 'Southern Softies', so Ditchling Beacon you can see that if you seek information on it from the various types of cyclist then you're likely to get responses like:-
Total Novice - this might kill you
Fatbloke - get a taxi
Mr Reasonable - it's doable with low enough gears but don't be afraid to have a rest or push for a while
Look at ME and Tremble - it only starts to get hard when you're on your third consecutive run and keeping above an 80" gear
Cockwomble - that's not a hill....followed by a list of real hills that they've generally completed in top gear, having a chat all the way up and laying down power that has tour riders full of envy. Fortunately a new ruling will mean that these riders have to attach a large dildo to the front of their bikes. Making them easier to spot, easier to avoid and allowing their 'Cockwombleness' to precede them everywhere.
Just a subjective view and YMMV