por·ten·tous 
(pôr-tĕntəs)
(pôr-tĕntəs)adj.
1. Of the nature of or constituting a portent; foreboding: "The present aspect of society is portentous of great change" (Edward Bellamy).
2. Full of unspecifiable significance; exciting wonder and awe: "Such a portentous and mysterious monster roused all my curiosity" (Herman Melville).
3. Marked by pompousness; pretentiously weighty.
por·tentous·ly adv.
por·tentous·ness n.
Usage Note: The last syllable of portentous is properly pronounced (-təs). However, under the influence of words like contentious and pretentious, sometimes this word is pronounced (pôr-tĕnshəs), as though it were spelled portentious. Both the (-shəs) pronunciation and the spelling with the i (which is occasionally seen in print) are widely considered to be mistakes.