ㄓㄥˋzhèngㄉㄤdāngㄓㄨㄥzhōng

  1. 正中西遊記·第一》:只見正當中石碣一行楷書大字花果山福地水簾洞洞天』。」

right in the midpoint, a bull's eye, to hit the nail on the head
en plein milieu