rain-wash vs washout

rain-wash and washout both are nouns.

Word	Noun	Adjective	Verb	Adverb
rain-wash	Yes	No	No	No
washout	Yes	No	No	No

As nouns, washout is a hypernym of rain-wash; that is, washout is a word with a broader meaning than rain-wash:

rain-wash: the washing away of soil or other loose material by rain
washout: the erosive process of washing away soil or gravel by water (as from a roadway)

Other hypernyms of rain-wash include wash.

rain-wash (noun)	washout (noun)
the washing away of soil or other loose material by rain	someone who is unsuccessful
	the erosive process of washing away soil or gravel by water (as from a roadway)
	the channel or break produced by erosion of relatively soft soil by water