prevailing westerly vs wester

prevailing westerly and wester both are nouns.

Word	Noun	Adjective	Verb	Adverb
prevailing westerly	Yes	No	No	No
wester	Yes	No	No	No

As nouns, wester is a hypernym of prevailing westerly; that is, wester is a word with a broader meaning than prevailing westerly:

prevailing westerly: the winds from the west that occur in the temperate zones of the Earth
wester: wind that blows from west to east

Other hypernyms of prevailing westerly include west wind.

prevailing westerly (noun)	wester (noun)
the winds from the west that occur in the temperate zones of the Earth	wind that blows from west to east