What will secure front of major clock feature is ornament (9)
I believe the answer is:
embellish
'ornament' is the definition.
(I know that ornament is a more specific form of embellish)
'what will secure front of major clock feature is' is the wordplay.
'what' becomes 'eh' (sound used to ask 'what?' or 'pardon?').
'will secure' is an insertion indicator (inserted letters are secured).
'front of' indicates taking the first letters (the letter at the front of the word).
'clock feature' becomes 'bell' (I can't explain this - if you can you should give a lot more credence to this answer).
The initial letter of 'major' is 'm'.
'm'+'bell'+'is'='mbellis'
'eh' enclosing 'mbellis' is 'EMBELLISH'.
Can you help me to learn more?
(Other definitions for embellish that I've seen before include "deck?" , "Add false details" , "Adorn" , "Add extra details to (story)" , "lard" .)