Understanding a relation is tricky (11)
I believe the answer is:
realisation
'understanding' is the definition.
(I know that realisation is a type of understanding)
'a relation is tricky' is the wordplay.
'tricky' indicates an anagram.
'a'+'relation'+'is'='arelationis'
'arelationis' is an anagram of 'REALISATION'.
(Other definitions for realisation that I've seen before include "Conversion (of asset) into cash (S, not Z)" , "Appreciation" , "Understanding" , "(Action of) forming a clear concept" , "Dawning (of an idea); achievement" .)