Old boy seeming discontented about dog at home hiding (9)

'hiding' is the definition.
(obscuring is a kind of hiding)

'old boy seeming discontented about dog at home' is the wordplay.
'old boy' becomes 'ob' (abbreviation).
'discontented' says to hollow out the word (remove centre letters).
'about' indicates putting letters inside.
'dog' becomes 'cur' (cur is a kind of dog).
'at home' becomes 'in' (similar in meaning).
'seeming' with its centre removed is 'sg'.
'cur'+'in'='curin'
'sg' placed around 'curin' is 'scuring'.
'ob'+'scuring'='OBSCURING'