IPA: //ˈmɪdnaɪt//
KK: /ˈmɪdˌnaɪt/
The time of night when the clock shows twelve o'clock, marking the middle of the night.
The party ended at midnight, and everyone went home.
Midnight is formed from "mid-" (meaning middle) and "night" (from Old English "niht", meaning the period of darkness). The word "midnight" refers to the middle of the night, specifically the time when one day ends and another begins.
Think of the 'middle' ('mid-') of the 'night' — that's why midnight is the time that falls in between the end of one day and the start of another.