Object emphatically struck ledge after repeatedly losing height (6)
I believe the answer is:
itself
'object emphatically' is the definition.
(emphatic way of referring to an object)
I don't understand the rest of the clue.
(Other definitions for itself that I've seen before include "Reflexive form for something already mentioned" , "See 1" , "Reflexive word - stifle (anag)" , "Pronoun used to reflect the object or for emphasis" , "individual personality" .)