Topographic feature of parts of Dartmoor (3)
I believe the answer is:
tor
'topographic feature' is the definition.
'tor' can be an answer for 'feature' (I have seen 'feature of Glastonbury' mean 'tor' so perhaps 'feature' could also mean 'tor'). I am not certain of the 'topographic' bit.
'of parts of dartmoor' is the wordplay.
'of' becomes 'o''.
'parts' is an insertion indicator (in the sense of cuts or separates).
'of dartmoor' becomes 'tr' (I can't explain this - if you can you should give a lot more credence to this answer).
'o' placed inside 'tr' is 'TOR'.
Can you help me to learn more?
(Other definitions for tor that I've seen before include "Rocky outcrop" , "Rot on a hill in Cornwall" , "Feature of Dartmoor" , "It rises" , "Rot on a peak in Devon" .)