1. Loud enough to cause (temporary) hearing loss
   - deafening, earsplitting, thundery 
2. Extremely ominous
   "world events of thunderous import"

See also: loud, thunder, unpropitious

• hydrogen iodide
• hydrogen ion
• hydrogen ion concentration
• hydrogen peroxide
• hydrogen sulfide
• hydrogen sulphide
• hydrogen-bomb
• hydrogenate
• hydrogenation
• hydrogenise
• hydrogenize
• hydrogenous
• hydrographer
• hydrographic
• hydrographical
• hydrography
• hydroid
• hydroiodic acid
• hydrokinetic
• hydrokinetics
• hydrolise
• hydrolith
• hydrolize
• hydrological
• hydrologist