The act or process of becoming wider or larger, or the state of being dilated.
From Latin dilatare (to spread out) + -ment suffix indicating a result or condition. The root comes from dis- (apart) and latus (wide), literally meaning to make wide.
This word is almost never used today—most people say 'dilation' instead—but it shows how English constantly creates and abandons synonyms, keeping only the ones that sound better or feel easier to use.
Complete word intelligence in one call. Free tier — 50 lookups/day.