Epibainō combines epi (upon) + bainō (to step, go). It means to step upon, mount, or embark — entering a boat, mounting an animal, or arriving at a place. It appears 6 times in the NT, in contexts ranging from the Palm Sunday entry to Paul's sea voyages.
The most theologically significant use is Matthew 21:5, quoting Zechariah 9:9: the king comes "mounted on [epibebēkōs] a donkey." This is the Triumphal Entry — Jesus deliberately fulfilling the prophecy of the humble king. He chooses the donkey over the warhorse. The act of epibainō on a humble beast rather than a stallion is a defining Christological statement: the Kingdom of God comes through humility, service, and sacrifice, not military might. The One who has authority over all creation dismounts from power to die for the powerless.