a.
1.
Hard, firm, compact, impenetrable.
2.
Dense, compact.
3.
Cubic.
4.
Strong, substantial, stable, sound, stout, firm, compact.
5.
Real, true, valid, just, weighty, firm, strong, substantial.
6.
Grave, profound, important, sound.
7.
Wealthy, rich, well-established, reliable, trustworthy, sound, safe.