Ugly skin, old, on us (7)
I believe the answer is:
hideous
'ugly' is the definition.
(similar in meaning)
'skin old on us' is the wordplay.
'skin' becomes 'hide' (hide is a kind of skin).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'on' says to put letters next to each other.
'hide'+'o'+'us'='HIDEOUS'
(Other definitions for hideous that I've seen before include "Ghastly" , "Extremely unpleasant" , "Horrible" , "revolting" , "Extremely ugly" .)