washout vs rain-wash

washout and rain-wash both are nouns.

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

As nouns, rain-wash is a hyponym of washout; that is, rain-wash is a word with a more specific, narrower meaning than washout:

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

washout (noun)	rain-wash (noun)
someone who is unsuccessful	the washing away of soil or other loose material by rain
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