In this way the cover is not hollow (5)
I believe the answer is:
solid
'is not hollow' is the definition.
('solid' is the opposite to 'hollow')
'in this way the cover' is the wordplay.
'in this way' becomes 'so'.
'the cover' becomes 'lid' (lid is a kind of cover).
'so'+'lid'='SOLID'
(Other definitions for solid that I've seen before include "Reliable - strong" , "Reliable - substantial - pure" , "Substantial - having three dimensions" , "Rock-hard" , "thick" .)