" portentous "

1: being or showing a sign of evil or calamity to come;

  * e.g., " ... an eerie and portentous stillness hung over the camp the night before the battle "

•  Synonyms : 

•  baleful,

•  dire,

•  direful,

•  doomy,

•  foreboding,

•  ill,

•  ill-boding,

•  inauspicious,

•  menacing,

•  minatory,

•  ominous,

•  sinister,

•  threatening

•  Antonyms : 

•  unthreatening

2: causing wonder or astonishment;

  * e.g., " ... in 1969 people regarded the first landing on the moon as a truly portentous event "

•  Synonyms : 

•  amazing,

•  astonishing,

•  astounding,

•  awesome,

•  awful,

•  eye-opening,

•  fabulous,

•  marvelous,

•  miraculous,

•  prodigious,

•  staggering,

•  stunning,

•  stupendous,

•  sublime,

•  surprising,

•  wonderful,

•  wondrous

•  Antonyms : 

• (N/A)