portentous in WordNet English dictionary

1. ominously prophetic
   fateful  foreboding  portentous 
   
2. puffed up with vanity
   "a grandiloquent and boastful manner"; "overblown oratory"; "a pompous speech"; "pseudo-scientific gobbledygook and pontifical hooey"- Newsweek
   grandiloquent  overblown  pompous  pontifical  portentous 
   
3. of momentous or ominous significance
   "such a portentous...monster raised all my curiosity"- Herman Melville; "a prodigious vision"
   portentous  prodigious