It is a moral Titan that struggles with this tyranny (15)
I believe the answer is:
totalitarianism
'this tyranny' is the definition.
(synonyms)
'it is a moral titan that struggles' is the wordplay.
'it is' becomes 'itis'.
'that struggles' is an anagram indicator.
'itis'+'a'+'moral'+'titan'='itisamoraltitan'
'itisamoraltitan' anagrammed gives 'TOTALITARIANISM'.
'with' acts as a link.
(Other definitions for totalitarianism that I've seen before include "Allowing no opposition" , "Dictatorship" .)