Deferentially tells you how someone does a thing: in a polite, respectful way that shows they are willing to accept another person’s opinion or judgment. They may speak deferentially, bow the head deferentially, or wait deferentially until the older person has finished. The action itself can be small; the adverb is about the spirit of it — giving way because you respect the other person, not because you are simply shy. It is a formal, slightly bookish adverb. In everyday talk, people more often say politely, respectfully, or with respect. It never means “later” or “after a delay.”