preposition
1.
a. : in control of
acted like a man on top of his job — Newsweek
b. : informed about
readers right on top of all the news that's fit to print — New York Times
2. : in sudden and unexpected proximity to
I was right on top of the coffin shop when the door opened — Margery Allingham
3. : in addition to : superadded to
writing on top of a regular job becomes a matter of stamina — N.M.Loomis