The word 'whammy' is a modern, playful creation with roots in onomatopoeia. It derives from 'wham,' a word that imitates the sound of a forceful impact, which entered English in the 1920s. The addition of the diminutive or noun-forming '-y' suffix transformed it into 'whammy,' a term for a metaphorical "strike" of bad luck or a jinx. Its popularity was cemented in the mid-20th century, especially through the comic strip "Li'l Abner," where the character Evil-Eye Fleegle could cast a "whammy" (a malevolent gaze), and by the phrase "double whammy," describing two setbacks occurring at once.

This is a simplex word. It is a 20th-century American English coinage, likely an alteration of the verb 'wham' (meaning to strike forcefully) combined with the suffix '-y' to form a noun. 'Wham' itself is imitative of the sound of a heavy blow.