2.PrepositionVery close to, in any orientation or in time.
"Living on top of one another in a refugee camp is stressful.; At peak times, a telephone operator must handle a number of calls, one on top of the next."
3.PrepositionIn addition to something else.
"[…] and on top of all that, I got a puncture!"
4.PrepositionFully informed about, and in control of, something; up to speed with.
"I have sorted out the problems and am now on top of the situation.; You will need to get on top of your nutrition in addition to training for washboard abs."