'Momentous' definitions:

Definition of 'momentous'

From: WordNet
adjective
Of very great significance; "deciding to drop the atom bomb was a very big decision"; "a momentous event"

Definition of 'Momentous'

From: GCIDE
  • Momentous \Mo*men"tous\, a. [Cf. L. momentosus rapid, momentary.] Of moment or consequence; very important; weighty; as, a momentous decision; momentous affairs. -- {Mo*men"tous*ly}, adv. -- {Mo*men"tous*ness}, n. [1913 Webster]