One who espouses; one who embraces or adopts the cause of another.(noun)
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Use "espouser" in a sentence
"He is a great espouser of new age thinking and has the air of a mystic."
"And then there was the espouser of doom himself: Roubini was known to be a perpetual pessimist, what economists call a “permabear.”"
"Neither the espouser of this model nor the regulators who ultimately bought into it had been contaminated by real world hands-on experiences with industrial equipment the proverbial armchair engineers"