soil erosion vs washout

soil erosion and washout both are nouns.

Word	Noun	Adjective	Verb	Adverb
soil erosion	Yes	No	No	No
washout	Yes	No	No	No

As nouns, washout is a hyponym of soil erosion; that is, washout is a word with a more specific, narrower meaning than soil erosion:

soil erosion: the washing away of soil by the flow of water
washout: the erosive process of washing away soil or gravel by water (as from a roadway)

Other hyponyms of soil erosion include wash.

soil erosion (noun)	washout (noun)
the washing away of soil by the flow of water	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