Mountain feature men note being worn by a river (8)
I believe the answer is:
colorado
'river' is the definition.
(Colorado is an example)
'mountain feature men note being worn by a' is the wordplay.
'mountain feature men' becomes 'color' (I am not sure about this - if you are sure you should believe this answer much more).
'note' becomes 'do' (musical note, as in do-re-mi).
'being worn by' means one lot of letters goes inside another (outside letters are worn by those on the inside).
'color'+'do'='colordo'
'colordo' going around 'a' is 'COLORADO'.
Can you help me to learn more?
(Other definitions for colorado that I've seen before include "Beetle whose larvae destroy potato plants" , "US state (with a beetle)" , "American state, capital Denver" , "in America?" , "US state has a cool road, oddly" .)