Undemanding hilltop not very high (7)
I believe the answer is:
lowbrow
'not very high' is the definition.
Both the definition and answer are adjectives. Maybe there's an association between them I don't understand?
'undemanding hilltop' is the wordplay.
'undemanding' becomes 'low' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'hilltop' becomes 'brow' (synonyms).
'low'+'brow'='LOWBROW'
Can you help me to learn more?
(Other definitions for lowbrow that I've seen before include "One preferring pop to classical" , "(Person) uninterested in intellectual pursuits" , "Uncultured (person)" , "Unsophisticated" , "not requiring much intelligence" .)