Conceal love for American that's ugly (7)
I believe the answer is:
hideous
'ugly' is the definition.
(similar in meaning)
'conceal love for american' is the wordplay.
'conceal' becomes 'hide' (synonyms).
'love' becomes 'o' (love means zero in tennis).
'for' says to put letters next to each other.
'american' becomes 'US' (United States).
'hide'+'o'+'us'='HIDEOUS'
'that's' acts as a link.
(Other definitions for hideous that I've seen before include "Extremely ugly" , "Extremely unpleasant" , "Horrible" , "Repulsive" , "Frightful" .)