Confusing relation by author losing heart (7)
I believe the answer is:
unclear
'confusing' is the definition.
(similar in meaning)
'relation by author losing heart' is the wordplay.
'relation' becomes 'uncle' (uncle is a kind of relation).
'by' is a charade indicator (letters next to each other).
'losing heart' suggests removing the centre.
'author' with its middle taken out is 'ar'.
'uncle'+'ar'='UNCLEAR'
(Other definitions for unclear that I've seen before include "Not certain" , "Imprecise, hazy" , "Indistinct" , "Ill-defined or not easily understood" , "Ambiguous" .)