Strong and sturdy (6)
'strong and sturdy' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for robust that I've seen before include "Down-to-earth" , "Physically strong" , "Sturdily built" , "Unlikely to break" , "Well-built" .)
(Other definitions for solid that I've seen before include "Dense" , "continuous" , "cone-shaped, say" , "Firm and stable" , "Weighty" .)