whitecap vs white horse

whitecap and white horse both are nouns.

Word	Noun	Adjective	Verb	Adverb
whitecap	Yes	No	No	No
white horse	Yes	No	No	No

As nouns, whitecap and white horse are synonyms defined as:

whitecap and white horse: a wave that is blown by the wind so its crest is broken and appears white

whitecap (noun)	white horse (noun)
a wave that is blown by the wind so its crest is broken and appears white	a wave that is blown by the wind so its crest is broken and appears white