First off...I am not a chemistry expert, but...
Broadly speaking, the -ous and -ic suffixes denote different valences (available electrons for bonding) of an atom or slightly different anion groups. The -ous suffix describes the lower-valence ion, and the -ic suffix, the higher-valence ion. But its different for different atoms, e.g. for copper it's +1 and +2, for iron +2 and +3...
So when you see compounds such as ferric somethingorother and ferrous somethingorother, they're different compounds. They're bonded differently, because iron is contributing 2 (ferrous) or 3 (ferric) electrons. Sometimes, as in my previous post, they're written as iron (II) and iron (III).
Another example of similar-sounding names but different compounds are nitric oxide (NO), sometimes used in the treatment of some cardiac conditions, and nitrous oxide (N2O), laughing gas.
That's the complete extent of my knowledge of chemical nomenclature. Hope I didn't get anything wrong.