The differences between いきなり, [急]{きゅう}に and [突然]{とつぜん} 突然 is more formal, seen in writings often but still fine for colloquial use Same as いきなり in meaning 唐突 is the same as 突然 but used with human behavior, not inanimate objects, trains, astroids, etc Example: 唐突なカミングアウト (unexpected and sudden coming out of a person about something)