IPA: /ˈæf.tə.nʊn/
KK: /ˈæf.tɚ.nun/
The time of day that comes after noon and lasts until evening, usually when the sun is still up.
We usually have lunch in the afternoon.
Afternoon → It is formed from "after" (from Old English "æfter", meaning following in time) and "noon" (from Old English "non", meaning the ninth hour of the day, which was around midday). The word "afternoon" refers to the time following noon, or the period of the day after midday.
Think of the time that comes 'after' ('after') 'noon' ('noon') — that's why afternoon means the time after midday.