Pretend to be ill? Stay with mum (8)
I believe the answer is:
malinger
'pretend to be ill?' is the definition.
(I've seen this before)
'stay with mum' is the wordplay.
'stay' becomes 'linger' (lingering is a kind of staying**).
'with' means one lot of letters go next to another.
'mum' becomes 'ma' ('ma' can be a synonym of 'mum').
'linger' after 'ma' is 'MALINGER'.
(Other definitions for malinger that I've seen before include "Feign illness to avoid work" , "Pretend to be ill to avoid work" , "Feign sickness to avoid work." , "To shirk work" , "Loaf about in germinal way" .)