'wishy-washy' originates from English, formed by the reduplicative pairing of 'wishy' and 'washy', where 'washy' was used to mean 'watery' or 'weak' (from the verb 'wash').

'washy' derives from the verb 'wash' (Old English 'wæscan'), implying something diluted or watered-down; the rhyming reduplication 'wishy-washy' arose in colloquial English in the 19th century to emphasize weakness or indecisiveness.

Initially it carried the sense of 'watery' or 'diluted', but over time it evolved into the figurative sense of 'lacking firmness or decisiveness' used today.