Vague relation has another, discontented (7)
I believe the answer is:
unclear
'vague' is the definition.
(similar in meaning)
'relation has another discontented' is the wordplay.
'relation' becomes 'uncle' (uncle is a kind of relation).
'has' means one lot of letters go next to another.
'discontented' suggests removing the centre (the word's contents are removed).
'another' with its middle taken out is 'ar'.
'uncle'+'ar'='UNCLEAR'
(Other definitions for unclear that I've seen before include "hard to understand" , "Imprecise, hazy" , "in clouds?" , "Not certain" , "Cloudy or opaque" .)