An old ambition crushed can be a terrible thing (11)
I believe the answer is:
Here is my best explanation:
'a terrible thing' is the definition.
'an old ambition crushed' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'crushed' indicates anagramming the letters.
'anoambition' with letters rearranged gives 'ABOMINATION'.
'can be' acts as a link.
(Other definitions for abomination that I've seen before include "A cause of disgust", "Cause of hatred or disgust", "Feeling of hatred or disgust" and "Action that is vile".)