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

See also: loud, thunder, unpropitious

• billion
• billion-dollar grass
• billionaire
• billionth
• billon
• billow
• billowing
• billowy
• billy
• billy buttons
• billy club
• billy goat
• Billy Graham
• Billy Mitchell
• Billy Sunday
• Billy Wilder
• billy-ho
• billycan
• billyo
• billyoh
• billystick
• bilobate
• bilobated
• bilobed
• bilocation