From Smith's Dictionary of Greek and Roman Biography and Mythology

BOOPIS

an epithet commonly given to Hera in the Homeric poems. It has been said, that the goddess was thus designated in allusion to her having metamorphosed to into a cow; but this opinion is contradicted by the fact that other divinities too, such as Euryphaessa and Pluto (Hesiod Theogony), are mentioned with the same epithet; and from this circumstance it must be inferred, that the poets meant to express by it nothing but the sublime and majestic character of those divinities.