Level up, housing sick boy (7)
I believe the answer is:
neville
'boy' is the definition.
'level up housing sick' is the wordplay.
'level' becomes 'even' (synonyms).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'housing' indicates putting letters inside.
'sick' becomes 'ill' (similar in meaning).
'even' reversed gives 'neve'.
'neve' enclosing 'ill' is 'NEVILLE'.
(Other definitions for neville that I've seen before include "- Longbottom, friend of Harry Potter" , "N Chamberlain, PM" , "Richard --, Earl of Warwick" .)