to take up and support (a cause, belief, etc)
For friendship makes us warmly espouse the interest of others — Henry Fielding
archaic or formal to marry (somebody)
You shall see what sort of a being I was cheated into espousing — Charlotte Brontë
espouser noun
[Middle English espousen via Old French from Latin sponsus, past part. of spondēre to promise, betroth]