IPA: /ˈnuːnˌtaɪm/
KK: /ˈnunˌtaɪm/
The period of time around noon, typically when the sun is at its highest point in the sky.
We usually have lunch at noontime.
Noontime is formed from "noon" (from Old English "non", meaning the ninth hour, which later came to refer to midday) and "time" (from Old English "tima", meaning a period or duration). The word "noontime" refers to the time of day that is around midday or noon.
Think of 'noon' as the time that originally referred to the ninth hour, which evolved to mean midday, combined with 'time' to remember that 'noontime' is the period around midday.