Noble big cat has walk displacing start of lunch (11)
I believe the answer is:
marchioness
'noble' is the definition.
(I've seen this before)
'big cat has walk displacing start of lunch' is the wordplay.
I cannot really see how this works, but
'walk' could be 'march' (marching is a kind of walking) and 'march' is located in the answer.
'of' could be 'o' and 'o' is present in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for marchioness that I've seen before include "Female aristocrat" , "Wife of a marquis" , "noble wife, perhaps" , "Noblewoman" , "Aristocratic lady" .)