To conceal a love for us is certainly not nice (7)
I believe the answer is:
hideous
'certainly not nice' is the definition.
I can't tell whether this defines the answer.
'to conceal a love for us' is the wordplay.
'to conceal' becomes 'hide' ('hide' can be a synonym of 'conceal').
'a love' becomes 'o' (love means zero in tennis).
'for' says to put letters next to each other.
'hide'+'o'+'us'='HIDEOUS'
'is' is the link.
Can you help me to learn more?
(Other definitions for hideous that I've seen before include "Extremely unpleasant" , "revolting" , "Ghastly" , "Repulsive" , "Extremely ugly" .)