1.  thunderous(s = adj.all) deafening, earsplitting, thundery - loud enough to cause (temporary) hearing loss;
Derived form noun thunder₁

2.  thunderous(s = adj.all) - extremely ominous; "world events of thunderous import"

1.  Producing thunder. [1913 Webster]
"How he before the thunderous throne doth lie." [1913 Webster]

2.  Making a noise like thunder; sounding loud and deep; sonorous. [1913 Webster]

thunderous, adj.
1 like thunder.
2 very loud.

Derivative:
thunderously adv. thunderousness n.