English word rainy day comes from English rainy (Pouring with rain; wet; showery.)

Detailed word origin of rainy day

Dictionary entry	Language	Definition
rainy	English (eng)	Pouring with rain; wet; showery.
rainy day	English (eng)	(idiomatic) A difficult period of need, when things do not go right.. Used other than with a figurative or idiomatic meaning: see rainy,‎.

Words with the same origin as rainy day