source: [カーニバル・ファンタズムの弓塚さつきが指差して仰天するGIF画像｜無料GIF画像検索 GIFMAGAZINE 698371]

SURPRISE, ASTONISH, ASTOUND, AMAZE, FLABBERGAST mean to impress forcibly through unexpectedness.

SURPRISE stresses causing an effect through being unexpected but not necessarily unusual or novel.

e.g. surprised to find them at home

ASTONISH implies surprising so greatly as to seem incredible.

e.g. a discovery that astonished the world

ASTOUND stresses the shock of astonishment.

e.g. too astounded to respond

AMAZE suggests an effect of bewilderment.

e.g. amazed by the immense size of the place

FLABBERGAST may suggest thorough astonishment and bewilderment or dismay.

e.g. flabbergasted by his angry refusal

verb with object

shock or greatly surprise:

〈人〉をびっくり仰天させる, 愕然とさせる (!しばしば受け身で; astonish, amazeより意味が強い)

e.g. her bluntness astounded him.

Middle English (as an adjective in the sense ‘stunned’): from astoned, past participle of obsolete astone (see astonish).