Firm, reliable (5)
I believe the answer is:
solid
I believe this is a double definition.
'firm' is the first definition.
(I know that firm can be written as solid)
'reliable' is the second definition.
(I've seen this before)
(Other definitions for solid that I've seen before include "Substantial - having three dimensions" , "Firm - sound - reliable" , "Shape with three dimensions" , "from one getting pushed around" , "Firm - substantial" .)